Community Hurricane Preparedness, 2nd Edition Produced by The COMET® Program Print Version Hazards Tropical Cyclone Threats Storm Surge What is Storm Surge? Influences SLOSH Using SDP Surge Mapping Local Forecasts Heavy Rains & Inland Flooding Influences Web Products River Forecast Centers National Forecasts Local Forecasts High Winds Wind Strength Effects After Landfall Local Forecasts Tornadoes Characteristics Damage Scale Local Forecasts Questions

Tropical Cyclone Threats

Bolivar Peninsula, TX before (top) and after (bottom) Hurricane Ike in 2008 The main weather hazards associated with tropical cyclones and hurricanes are: Storm surge Flooding from heavy rain High winds Tornadoes This section will discuss each of the main hurricane hazards in more detail. While more intense storms are often the most dangerous, direct impacts depend on many factors besides

intensity, including where the storm strikes. A less intense storm that hits a densely populated area has the potential to cause more damage and injuries or deaths than a stronger one that goes over a rural area. For example, Hurricane Ike (2008) was a Category 2 hurricane made landfall near Galveston Bay, Texas where it caused at least 20 deaths, many of which occurred in the 15-20 ft (4.6-6 m) storm surge. An additional 64 indirect deaths occurred due to pre-existing medical conditions, electrocution, and carbon monoxide poisoning. Hurricane Frances (2004), also a Category 2 hurricane, ranks in the top 10 most damaging storms with costs in the billions of dollars.

In addition to direct impacts, hurricane hazards can have indirect adverse consequences. For example, many hurricane-related deaths and injuries result from carbon monoxide poisoning or from fires started by downed power lines or sparks from generators and candles used when the electricity fails.

A fire burns in an area of New Orleans impacted by Hurricane Katrina (2005) Heart attacks and accidents from downed power lines, ruptured gas lines, or dealing with post-storm debris frequently occur during the clean-up phase. And depending on the industrial facilities in your area, hurricane damage might cause chemical spills that could make the disaster even worse.

An environmental specialist disposes of chemicals spilled by Hurricane Rita (2005) Although many factors of a landfalling hurricane or tropical storm are out of our control, community planning and preparedness efforts can play a critical role in determining the magnitude of the impact on a community. Other factors that may determine the outcome include:

• • • • •

Community preparedness: Effective emergency management planning efforts, open communication lines between stakeholders, and a responsive citizenry play a large role in determining how a storm impacts that community. Prior community mitigation efforts: For example, strong building codes that are rigorously enforced can limit the damage inflicted. Previous community experience with storms: A community that has not been hit by a hurricane recently may become a bit complacent about future events. Time of day: Evacuation orders may be more successful depending on when they are issued Storm behavior: Rapid intensification and/or changes in storm speed/direction prior to landfall may change your planning assumptions.

Storm Surge

Storm surge from Hurricane Ike (2008) Along the coast, storm surge is the greatest threat to life and property. In the past, large death tolls have resulted from the rise of the ocean associated with many of the major hurricanes that have made landfall. Hurricane Katrina (2005) is a prime example of the damage and devastation that can be caused by surge. Approximately 1500 persons lost their lives during Katrina and most of those deaths have been attributed to storm surge.

What is Storm Surge? Storm surge is the abnormal rise in sea level generated by a hurricane or other intense storm, over and above the predicted or normal astronomical tide. It is caused mainly by hurricane winds shoving the ocean water up over the coast, although low pressure in the eye also contributes a much smaller amount.

The height of water level rise due to storm surge is the difference at the coast between the observed level of the sea surface and the level that would have occurred in the absence of the tropical cyclone. So, as shown in the example below, the storm surge at the coast would be 20 feet (6 m) above normal tide levels. As the elevation increases, the depth of the water decreases, but land areas up to 20 feet in elevation (in this case) would be vulnerable to flooding.

"Storm tide" is the water level rise due to the combination of the storm surge and the astronomical tide, so water levels will be especially high when the storm surge occurs at the same time as high tide. As an example, during Hurricane Katrina (2005) the storm tide along the Mississippi coast was higher than 20 feet in most places, and the water was able to penetrate inland as far as 6 to 12 miles from the coast.

As the surge comes in, prior to the eye making landfall, the rising water often acts as a "bulldozer", destroying homes and leveling property along the coast. Beaches, cars, trees, and anything in the path of the rising water are washed away. Low lying areas are inundated and severe flooding occurs as the water from the ocean travels inland.

Beach erosion and destroyed seawall in Florida after Hurricane Jeanne (2004)

Influences The level of storm surge during a storm is influenced by:

• • • • • • • •

Size and extent of storm’s wind field ("radius of maximum winds") Strength of storm winds (see animation) Storm’s forward speed Storm track Storm’s central pressure (contribution of pressure to total storm surge is small compared to wind) Landfall location Coastal elevation (much of the densely populated Atlantic and Gulf coastlines are less than 10 feet [3 m] above mean sea level, making them especially vulnerable.) Shape and characteristics of the coast (bays, rivers, etc.)

In addition, surge inundation in an area is also affected by the underwater topography ("bathymetry") off the coast–in particular, the slope of the continental shelf. A shallow slope will potentially produce a greater storm surge than a steep shelf. For example, a Category 5 storm hitting the Georgia coastline, which has a very wide and shallow continental shelf, may produce a 20-foot storm surge, while the same hurricane in a place like West Palm Beach, Florida, where the continental shelf drops off very quickly, might see only an 8 or 9–foot surge.

Battering wind waves on top of the total storm tide may increase damage along the coast. Water weighs approximately 1,700 pounds per cubic yard (~1,000 kg/cubic meter); extended pounding by frequent waves can demolish any structure not specifically designed to withstand such forces.

Additionally, currents created by tides combine with the waves to severely erode beaches and coastal highways. Buildings that survive hurricane winds can be damaged if their foundations are undermined and weakened by erosion.

Although elevated, this house in North Carolina could not withstand the 15 ft (4.5 m) of storm surge that came with Hurricane Floyd (1999)

Beachfront road and boardwalk damaged by Hurricane Jeanne In confined harbors, the combination of storm tides, waves, and currents can also severely damage marinas and boats. And in estuaries and bayous, salt water intrusion endangers public health and can send animals, such as snakes and alligators, fleeing from flooded areas.

Damaged boats in a marina

SLOSH What is SLOSH? SLOSH (Sea, Lake and Overland Surges from Hurricanes) is a computerized model developed for emergency managers and the scientific community and run by the NHC to estimate storm surge potential resulting from historical, hypothetical, or predicted hurricanes. The SLOSH Display Program (SDP) is the software provided to emergency managers and other users to visualize the data produced by the NHC. Graphical output from the SDP displays color-coded storm surge heights for a particular area in feet, either above a specific reference level (National Geodetic Vertical Datum of 1929 [NGVD29] or the North American Vertical Datum of 1988 [NAVD88]), or displayed in feet above ground level (inundation).

Example of a SLOSH Model animation for Hurricane Gustav (2008)

The calculations and predictions incorporate local bay and river configurations, water depths, bridges, barrier systems, levees, roads and other physical features. However, the SLOSH model cannot fully resolve small scale features.

Using SDP The SLOSH Display Program (SDP) is only one of several tools used by emergency management agencies to determine who is at risk and should evacuate. The exact location and timing of a hurricane’s landfall is crucial in determining which areas will be inundated by the storm surge. Small changes in track, intensity, size, forward speed, and landfall location can have huge impacts on storm surge. The forecast track and intensity of a tropical cyclone are subject to large errors, thus a single simulation (deterministic run) of the SLOSH model does not always provide an accurate depiction of the true storm surge vulnerability. NHC, therefore, employs an ensemble approach by using thousands of SLOSH simulations for each geographic area. These ensemble simulations accurately account for the full spectrum of storm characteristics by including different:

Directions of motion Landfall locations Intensities Storm sizes Forward speeds

The results of these simulations are composited (grouped) into storm surge atlases or maps. Available SLOSH ensemble products include the MEOW, MOM, and probabilistic storm surge products: The MEOW (Maximum Envelope of Water) provides an estimate of the potential inundation from a hurricane of a given category moving in a given direction at a given forward speed. MEOWs are precomputed products available anytime. The MEOW plans for the worst case scenario. (Note: MEOW also refers to Maximum Envelope of Winds, which is a different hurricane product produced by the Inland Wind Model.)

Example MEOW graphic for all hypothetical Category 2 storms that move in a northwest direction through the New Orleans Basin at a forward speed of 15 mph. This MEOW is closest to the characteristics of Hurricane Gustav (2008), which made it a useful decision-making tool prior to that storm making landfall.

MOM (Maximum of Maximums or Maximum of MEOW) displays a composite of the maximum storm surge height for all hurricanes of a given strength/intensity (i.e. Category, 1, 2, 3, 4, and 5 on the Saffir– Simpson Hurricane Wind Scale). There are only 5 MOMs per geographical region, one per Saffir– Simpson Hurricane Wind Scale category. MOMs are pre-computed products available anytime.

Example MOM graphic showing the maximum storm surge height for all hypothetical Category 2 storms for this region. Unlike the MEOW, it includes all forward speeds and directions. Probabilistic Storm Surge product (P-Surge) is produced whenever a hurricane watch or warning is in effect for any portion of the United States coastline. It is the result of multiple SLOSH simulations based on perturbations (alternate scenarios) of the operational NHC track, intensity, and size forecast. The perturbations used are based on the performance (accuracy) of previous year’s forecasts. P-Surge is available with other routine products on the NHC website.

Example of P-Surge graphic for Hurricane Gustav (2008), 24 hours before landfall

Surge Mapping Surge maps are one tool that can assist with planning and preparing for tropical cyclones by providing a snapshot of a community’s vulnerability to storm surge for each category of hurricane and are used to create evacuation zones.

The Hurricane Evacuation Study (as discussed in the Emergency Management section) for a given community contains surge maps, based on SLOSH MOMs, to provide an analysis of surge vulnerability. The SLOSH MOMs provide the maximum potential inundation for a particular local area. These maps are combined with other data such as census information, transportation studies, behavioral studies, and critical infrastructure locations to create evacuation zones. Evacuation zones account for surge and other hazards and can be used as an effective tool for communicating who needs to evacuate due to the threat of storm surge during landfalling hurricanes.

The graphics below are storm surge maps for Category 2 and Category 4 storms hitting New York.

New tools, such as Google Earth, can be useful for providing an understanding of the possible impacts from flooding. For example, this image of Manhattan, NY has been colorized to show all elevations under 20 ft (6 m), so it gives a sense of what 20 feet of storm surge could inundate in the city.

Local Forecasts Your local NWS Weather Forecast Offices (WFOs) monitor your weather around-the-clock. (To find your local WFO, go to http://www.weather.gov/organization.php.) In addition to the forecast issued two to four times daily, the local WFO coordinates closely with NHC to provide local forecast products and warnings. One of these products is the Hurricane Local Statement (HLS). The HLS is a valuable product that can be used as a tool to monitor several different threats (not just surge) and potential impacts to your area. It includes:

• • • • • •

Counties, parishes, or cities affected Watches and/or warnings in effect Recommended precautionary actions Storm surge and storm tide information Present winds and the expected time of onset of tropical storm or hurricane-force winds Tornado, flood, flash flood, rip current, beach erosion, and inland high wind potential

Below is an example of the storm surge portion of an HLS:

...STORM SURGE AND STORM TIDE... TIDE LEVELS REPORTED BETWEEN 330 AND 400 PM SATURDAY: HOUSTON SHIP CHANNEL/MANCHESTER – 10.4 FEET EAGLE POINT – 7.7 FEET PIER 21 – 5.8 FEET PLEASURE PIER – 5.2 FEET FREEPORT – 2.7 FEET

STORM SURGE FLOODING PERSISTS ALONG THE SHORE OF GALVESTON BAY AND ON THE BOLIVAR PENINSULA. THIS INCLUDES NEIGHBORHOODS NEAR THE SHORE OF CLEAR LAKE...AND THE COMMUNITIES OF SMITH POINT...LA PORTE...SEABROOK...KEMAH...BACLIFF...SAN LEON...AND SURROUNDING AREAS. TIDE LEVELS RANGE FROM 7 TO 11 FEET IN THESE AREAS. BOLIVAR PENINSULA IS COVERED WITH WATER. RAINFALL-INDUCED FLOODING OVER THE LAND AND IN CREEKS AND BAYOUS MUST DRAIN OUT INTO GALVESTON BAY WHICH WILL KEEP WATER LEVELS ON THE BAY ABOVE NORMAL FOR AN EXTENDED PERIOD OF TIME. TIDE LEVELS WILL ONLY SLOWLY SUBSIDE IN THESE AREAS THROUGH TONIGHT...AND WILL NOT RECOVER TO NEAR NORMAL LEVELS UNTIL SUNDAY MORNING.

Community Considerations

• • •

What requirements are in place for new construction in flood hazard areas in your community? In your community, what depth is necessary for structure foundations to protect against erosion that will be caused by storm surge in coastal flood hazard areas? What actions should you advise boat and marina owners to take in the event of a major hurricane?

Heavy Rains & Inland Flooding

Flooding in Asheville, NC, 690 miles (1110 km) north of where Hurricane Frances (2004) made landfall in Florida Widespread rainfall of 6 inches (15 cm) or more is common during landfall, frequently producing deadly and destructive floods. Heavy rain from these storms can last for days. Such floods have been one of the primary causes for tropical cyclone-related fatalities over the past 30 years, including many who were children. Heavy rainfall isn’t confined to the coast. Large amounts of rain can occur thousands of miles inland. Much of the damage in 4 of the 20 costliest tropical cyclones resulted from inland floods caused by torrential rain, rather than strong winds. For example, Tropical Storm Allison (2001) made landfall with 50 mph (80 km/h) winds but dumped over 40 inches (102 cm) of rain in Texas. As it moved back into the Gulf and then turned northeast, heavy rains along its path contributed to billions of dollars in damage and 41 deaths.

In addition to localized and urban flooding, there can be other impacts from the heavy rain associated with tropical systems. This includes river flooding, dam breaks, lake overflow, and mudslides.

Influences Risk from flooding depends on a number of factors: Speed of the storm Size of the storm Persistent rain bands Interactions with other weather systems, such as cold fronts Terrain Ground saturation

Rainfall is generally greatest with slow moving storms (less than 10 mph or 16 kph). To estimate the total rainfall in inches, one rule of thumb is to divide 100 by the forward speed of the hurricane in miles per hour (100/forward speed = estimated inches of rain). Your local Weather Forecast Office (WFO) may have a more accurate estimation method for your area. So, while some tropical storm hazards like tornadoes and high winds generally become less of a threat as a storm moves farther inland (although there are exceptions), heavy rains frequently continue and may even intensify as tropical cyclones merge with other storm systems. In mountainous regions, the remaining storm can be forced up the terrain. As the air rises, it cools, and even more moisture condenses into rain drops, adding to the precipitation amounts. And as the rain falls, mountain streams quickly fill, and flash floods become the major threat along with mudslides on the steep, saturated slopes.

House damaged by debris flow from the Peek’s Creek flood Hurricane Ivan (2004) is another example of a storm that produced extensive inland flooding, especially as it encountered higher terrain. As the storm interacted with the topography of the Appalachian Mountains, Ivan produced extensive and dangerous flooding in many areas of the Southeast, with some locations in North Carolina receiving more rainfall than fell on the coast as the storm made landfall. Western North Carolina had been saturated just a week and a half earlier from the remnants of Hurricane Frances. The resulting floods, mudslides, and landslides caused major damage and debris that swept down Peek’s Creek, NC, carried off 15 houses and killed 5 people.

Web Products The NWS Advanced Hydrologic Prediction Service (AHPS) monitors more than 3000 river gages across the United States, including American Samoa, Guam, Puerto Rico and the Virgin Islands. Many of these sites are USGS gages that report on intervals of an hour or less. This helps the NWS monitor these gages 24 hours a day, 7 days a week for the threat of flooding. On this page, we’ll discuss NWS Web-based products available from www.weather.gov that provide flood information. Some similar products (also derived from AHPS data) are also available via the HURREVAC model interface discussed in the Emergency Management section. The "Water" tab on www.weather.gov goes to www.weather.gov/ahps which displays a map (image below) that shows the current flood stage for all of the river gauges in the country. Green data points mean the river is below flood stage, yellow indicates stations near flood stage, and orange, red, and purple squares flag rivers above flood stage. Note that this graphic depicts river flooding, not flash floods.

Example of flood stage map Clicking on an individual square will bring up a local map (shown below). Squares indicate stations that have only observations, while the diamonds denote stations that also have forecast information.

Example of a local river gauge display Clicking one of the symbols will display a graph (below) of the past hourly observations (blue line) and the forecast (dotted green line) of the river height at that location for the next several days. The different colors of the background represent various high water levels, with the orange, red, and purple backgrounds highlighting flood stages. In this particular example, recent rains resulted in moderate flooding that was forecast to fall below flood stage on November 24th.

Example of a plot of observations and forecast conditions for a single river gauge In addition to the river forecasts, you can also look at what impacts may occur as the result of particular river levels. Scrolling down the screen below the river forecast graph, you’ll find a map (below) displaying the location of the river gauge. To the left of the map is a list of record river crests. Below the map is a list of impacts when the river reaches a particular value. This example shows a historic crest of 33.9 ft (10.3 m) occurred on May 20, 1943.

Example of a information about past flood events in the area of this river gauge

River Forecast Centers Thirteen NWS River Forecast Centers (RFCs) provide river and flood forecasts and warnings for the protection of lives and property, as well as basic hydrologic forecast information for the nation’s environmental and economic well being.

Map of the 13 NWS River Forecast Centers The basic functions of the RFCs are to supply: Continuous hydrometeorological data assimilation, river basin modeling, and hydrologic forecast preparation Technical support and interaction with other NWS offices Technical support and interaction with outside water management agencies and users Applied research, development, and technological implementation

RFCs provide hydrologic guidance for time scales that vary from hours (flash flood guidance and support to Local Flood Warning Systems), to days (traditional flood forecasts), to weeks (snowmelt forecasts), to months (seasonal water supply).

To go to the webpage for your River Forecast Center, start at http://water.weather.gov/ahps/rfc/rfc.php and click the portion of the map for your area. You’ll then have access to several products (see example below) that range from observed conditions to forecasts of both rivers and precipitation. Some of the displays available on the RFC websites are the same as the local river displays available from the www.weather.gov website, but the RFCs also provide additional data, so it’s worth getting familiar with what’s available on the various sites.

Example of a display of 24-hour accumulated precipitation as recorded by radars, available from the MiddleAtlantic RFC (http://www.erh.noaa.gov/marfc/)

National Forecasts For more detail on the quantity of precipitation expected and the potential for excessive rain that could cause flooding, go to the NWS Hydrometeorological Prediction Center (HPC) Website (http://www.hpc.ncep.noaa.gov/) and select the Quantitative Precipitation Forecast (QPF) graphic (example below). These graphics give precipitation forecasts for various time periods up to a 5–day total.

Example plot of 24-hour forecasted precipitation quantities (QPF). HPC provides guidance, analysis, forecast products, real-time weather model diagnostics discussions, and surface pressure and frontal analyses. Additionally, when NHC drops responsibility for a tropical system after it makes landfall, HPC takes responsibility for issuing public advisories four times a day. Below is an example of an HPC public advisory for the inland remnants of a tropical storm.

PUBLIC ADVISORY NUMBER 29 FOR REMNANTS OF IDA NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD AL112009 1000 PM EST TUE NOV 10 2009 ...TROPICAL RAINS SPREAD NORTHEAST ACROSS THE MID-ATLANTIC... FLOOD AND FLASH FLOOD WATCHES...WARNINGS...AND ADVISORIES REMAIN IN EFFECT ALONG PORTIONS OF THE GULF COAST...NORTHEASTWARD ACROSS THE SOUTHEAST...AND NORTHWARD INTO THE MID-ATLANTIC AND TENNESSEE VALLEY.

WIND AND LAKE WIND ADVISORIES ARE IN EFFECT ACROSS THE SOUTHEASTERN UNITED STATES. FOR INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE OFFICE AT WWW.WEATHER.GOV.

AT 1000 PM EST...0300 UTC...THE CENTER OF REMNANTS OF IDA WAS LOCATED NEAR LATITUDE 30.8 NORTH...AND LONGITUDE 85.3 WEST...OR 60 MILES...95 KM...WEST-NORTHWEST OF TALLAHASSEE FLORIDA AND 120 MILES...195 KM...SOUTH OF COLUMBUS GEORGIA.

THE LOW PRESSURE CENTER WILL CONTINUE ITS EASTWARD TRACK ALONG THE FLORIDA PANHANDLE TUESDAY NIGHT. BY THURSDAY MORNING...THE LOW IS EXPECTED TO REDEVELOP AND STRENGTHEN OFF THE CAROLINA COAST.

MAXIMUM SUSTAINED WINDS ARE NEAR 20 MPH...30 KM/HR...WITH HIGHER GUSTS. THE MINIMUM CENTRAL PRESSURE IS 1006 MB...29.71 INCHES. SELECTED STORM TOTAL RAINFALL IN INCHES THROUGH 10 PM EST ...ALABAMA... FOLEY 0.5 ESE SUMMERDALE 2.5 ESE ELBERTA 3.1 SSW BREWTON 3 SSE ATMORE 12 N OPELIKA 11.0 S . .[deleted locations for brevity] .

...MISSISSIPPI... WIGGINS 6 E WAYNESBORO 2 W PASCAGOULA 3 NE VANCLEAVE 4.1 NNW NEW AUGUSTA 1 N OCEAN SPRINGS 3.3 E MOSS POINT 10.2 NE BUCKATUNNA SHUBUTA CRANDALL 12 N KEESLER AFB/BILOXI

6.61 6.13 5.84 5.50 5.41 5.40

4.08 4.05 3.42 3.34 3.28 3.24 3.10 3.10 2.98 2.95 2.49

BY THURSDAY EVENING...ADDITIONAL RAINFALL AMOUNTS OF 4 TO 8 INCHES...WITH ISOLATED AMOUNTS OF UP TO 12 INCHES...ARE EXPECTED ACROSS THE SOUTHEAST AND INTO THE MID-ATLANTIC.

...SUMMARY OF 1000 PM EST INFORMATION... LOCATION...30.8N 85.3W MAXIMUM SUSTAINED WINDS...20 MPH PRESENT MOVEMENT...EAST OR 090 DEGREES AT 16 MPH MINIMUM CENTRAL PRESSURE...1006 MB

THE NEXT ADVISORY ON THIS SYSTEM WILL BE ISSUED BY THE

HYDROMETEOROLOGICAL PREDICTION CENTER AT 400 AM EST. PLEASE REFER TO YOUR LOCAL NATIONAL WEATHER SERVICE OFFICE FOR FURTHER INFORMATION ON THIS STORM.

GERHARDT FORECAST POSITIONS INITIAL 11/0300Z 30.8N 12HR VT 11/1200Z 30.8N 24HR VT 12/0000Z 31.7N 36HR VT 12/1200Z 33.1N 48HR VT 13/0000Z 33.5N

85.3W 84.3W...EXTRATROPICAL 79.7W...EXTRATROPICAL 77.3W...EXTRATROPICAL 76.0W...EXTRATROPICAL

Local Forecasts The possibility of heavy rain after a hurricane moves inland makes monitoring weather conditions and maintaining contact with your local WFO very important. Keep an eye out for their regular forecasts and the HLS. Below is an example of the inland flooding portion of an HLS

...INLAND FLOODING... FLOOD WARNINGS ARE IN EFFECT FOR THE FOLLOWING WATERSHEDS: LOWER WHITE OAK BAYOU MIDDLE AND LOWER GREENS BAYOU BUFFALO BAYOU KEEGANS BAYOU SAN JACINTO RIVER BELOW LAKE HOUSTON LOWER SPRING CREEK PEACH CREEK LUCE BAYOU

NUMEROUS STREAMS AND BAYOUS ARE THREE-QUARTERS FULL OR CLOSE TO BANK FULL. PLEASE CONSULT THE LATEST FLOOD AND FLASH FLOOD WARNINGS FOR AREA RIVERS...CREEKS...AND BAYOUS. A FLOOD WATCH REMAINS IN EFFECT THROUGH SUNDAY. RAIN BANDS ASSOCIATED WITH TROPICAL STORM IKE WILL AFFECT NORTHERN PORTIONS OF HARRIS AND LIBERTY COUNTIES THIS EVENING. A COLD FRONT WILL MOVE THROUGH THE AREA SUNDAY GENERATING ADDITIONAL SHOWERS AND THUNDERSTORMS.

ADDITIONAL RAINFALL AMOUNTS OF 1/2 TO 1 INCH...WITH ISOLATED ADDITIONAL TOTALS OF 2 TO 4 INCHES CAN BE EXPECTED THROUGH SUNDAY. ANY RAINFALL WILL EXACERBATE THE EXISTING FLOODING PROBLEMS.

Community Considerations What areas within your community would be at risk from flooding or mudslides if you had large amounts of rain in a 24-hour period? What might you expect if the ground was already saturated from rains a few days before the hurricane made landfall?

High Winds

Damaging winds begin well before the hurricane eye makes landfall. Even tropical storm-force winds can be unsafe, and wind gusts just add to the destructive power of storms. For this reason, emergency managers plan on having their evacuations complete and their personnel sheltered before the onset of tropical storm-force winds, not hurricane-force winds.

Example of a wind speed probability forecast produced by NHC

Wind Strength Once winds exceed 73 mph (63 kt), a storm’s intensity is expressed using the Saffir-Simpson Hurricane Wind Scale, which categorizes storms by wind speed and potential damage. Note that a Category 1 hurricane has lower speed winds compared to storms in higher categories. A Category 4 hurricane would usually (but not always) be expected to cause 100 times the damage of a Category 1 storm. A "major" hurricane is classified as Category 3 or greater. As indicated in the Basics section, the strongest winds usually occur on the right side of the eyewall of the hurricane.

Category

1

2

3

Definition–Effects Winds: 74-95 mph (119-153 km/hr ) Very dangerous winds will produce some damage. Some damage to building structures could occur, primarily to unanchored mobile homes (mainly pre-1994 construction). Some damage is likely to poorly constructed signs. Loose outdoor items will become projectiles, causing additional damage. Persons struck by windborne debris risk injury and possible death. Numerous large branches of healthy trees will snap. Some trees will be uprooted, especially where the ground is saturated. Many areas will experience power outages with some downed power poles.

Winds: 96-110 mph ( 154-177 km/hr) Extremely dangerous winds will cause extensive damage. Some roofing material, door, and window damage of buildings will occur. Considerable damage to mobile homes (mainly pre-1994 construction) and poorly constructed signs is likely. A number of glass windows in high rise buildings will be dislodged and become airborne. Loose outdoor items will become projectiles, causing additional damage. Persons struck by windborne debris risk injury and possible death. Numerous large branches will break. Many trees will be uprooted or snapped. Extensive damage to power lines and poles will likely result in widespread power outages that could last a few to several days.

Examples

Hurricane Dolly (2008) brought Category 1 winds and impacts to South Padre Island, Texas.

Hurricane Frances (2004) brought Category 2 winds and impacts to coastal portions of Port St. Lucie, Florida with Category 1 conditions experienced elsewhere in the city.

Hurricane Ivan (2004)Winds: 111-129 mph (178-208 km/hr) Dangerous winds will cause extensive damage.brought Category 3 Some structural damage to houses and buildings will occur with a minorwinds and impacts to amount of wall failures. Mobile homes (mainly pre-1994 construction) and coastal portions of poorly constructed signs are destroyed. Many windows in high rise buildings Gulf Shores, Alabama will be dislodged and become airborne. Persons struck by windborne debris with Category 2 risk injury and possible death. Many trees will be snapped or uprooted and conditions block numerous roads. Near total power loss is expected with outages that experienced could last from several days to weeks.elsewhere in this city. Winds: 130-156 mph ( 209-251 km/hr) Devastating damage will occur.Hurricane Charley Some wall failures with some complete roof structure failures on houses will (2004) brought occur. All signs are blown down. Complete destruction of mobile homesCategory 4 winds and

4

5

occur. All signs are blown down. Complete destruction of mobile homes

Category 4 winds and

(primarily pre-1994 construction). Extensive damage to doors and windows is likely. Numerous windows in high rise buildings will be dislodged and become airborne. Windborne debris will cause extensive damage and persons struck by the wind-blown debris will be injured or killed. Most trees will be snapped or uprooted. Fallen trees could cut off residential areas for days to weeks. Electricity will be unavailable for weeks after the hurricane passes.

impacts to coastal portions of Punta Gorda,Florida with Category 3 conditions experienced elsewhere in the city.

Winds: 157+ mph ( 252+ km/hr ) Catastrophic damage will occur. Complete roof failure on many residences and industrial buildings will occur. Some complete building failures with small buildings blown over or away are likely. All signs blown down. Complete destruction of mobile homes (built in any year). Severe and extensive window and door damage will occur. Nearly all windows in high rise buildings will be dislodged and become airborne. Severe injury or death is likely for persons struck by wind-blown debris. Nearly all trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months.

Hurricane Andrew (1992)brought Category 5 winds and impacts to coastal portions of Cutler Ridge, Florida with Category 4 conditions experienced elsewhere in south Miami-Dade County.

Effects Hurricane winds not only damage structures, but the barrage of debris they carry is dangerous to anyone unfortunate enough (or unwise enough!) to be caught out in them. High-rise buildings are also vulnerable to hurricane-force winds, particularly at the upper levels since wind speed tends to increase with height. For example, winds at the top of a 30-story building will average about 20 mph (32 km/hr), or one SaffirSimpson category, higher than at the surface.

Windows in high-rise buildings are often blown out during tropical cyclones, so the areas around these buildings can be very dangerous. Planning activities should account for the effects from high winds in determining where citizens are encouraged to shelter-in-place during a storm. Additionally, preparations for re-entry activities may need to factor in protecting residents from any areas with high rise buildings that may have been damaged by high winds.

After Landfall Wind speed usually decreases significantly within 12 hours of landfall (see the graph below). This is partly because the roughness of the terrain increases friction, slowing the air. Also, once the storm is over land, it is usually cut off from the heat and moisture sources that sustain it. Note that, after about 24 hours after landfall, the wind impacts from a tropical storm can be similar to those from a hurricane.

Wind gusts (as opposed to the sustained winds shown in the graph) may actually increase after landfall because there is more turbulence over land, which mixes faster air to the surface in short bursts. Note too that winds can stay above hurricane strength well inland. For example, Hurricane Hugo (1989) battered Charlotte, North Carolina, which is 175 miles (280 km) inland, with gusts to nearly 100 mph (90 kt). Hurricane Ike (2008) became an extratropical cyclone with hurricane-force winds after it moved well inland, causing widespread damage across the Ohio Valley and lower Great Lakes and on into Ontario.

Local Forecasts The daily forecasts and HLS issued by your local WFO will provide important information on the wind threat. Below is an example of the wind forecast in an HLS:

...WIND IMPACTS... TROPICAL STORM FORCE WINDS...39 MPH OR GREATER...ARE EXPECTED TO REACH THE UPPER TEXAS COAST AROUND NOON FRIDAY AND SPREAD INLAND TO THE INTERSTATE 10 CORRIDOR BY LATE AFTERNOON. THE TROPICAL STORM FORCE WINDS ARE THEN EXPECTED TO PUSH NORTHWARD ACROSS THE REMAINDER OF SOUTHEAST TEXAS BY AROUND MIDNIGHT.

THE ONSET OF HURRICANE FORCE WINDS ARE EXPECTED AT THE COAST LATE FRIDAY EVENING. HURRICANE FORCE WINDS ARE EXPECTED TO SPREAD INLAND ACROSS THE EASTERN 1/4 PORTION OF SOUTHEAST TEXAS...GENERALLY EAST OF INTERSTATE 45...THROUGHOUT THE REMAINDER OF FRIDAY NIGHT AND INTO SATURDAY AFTERNOON. ASSUMING THE RITA FOLLOWS THE FORECAST TRACK ...LISTED BELOW ARE ESTIMATED WINDS SELECTED COUNTIES CAN EXPECT. KEEP IN MIND THEY WILL BE HIGHER TO THE EAST AND NOT AS STRONG TOWARD MATAGORDA BAY:

COUNTY SUSTAINED WINDS (MPH) PEAK GUST (MPH) CHAMBERS 125 155 LIBERTY 115 140 POLK 100 130 GALVESTON 90 110 HARRIS 75 90 SAN JACINTO 75 90 TRINITY 75 90 BRAZORIA 60 80 WHARTON 55 70 BRAZOS 55 65 MATAGORDA 45 60

AN INLAND HURRICANE WATCH REMAINS IN EFFECT FOR ALL OF SOUTHEAST TEXAS. THIS MEANS SUSTAINED WINDS GREATER THAN 74 MPH ARE POSSIBLE OVER ALL OF SOUTHEAST TEXAS. THE IMPACTS FOR SUSTAINED WINDS OF 70 TO 90 MPH WITH GUSTS 100 TO 110 MPH ARE AS FOLLOWS... VERY DANGEROUS WINDS WILL PRODUCE WIDESPREAD DAMAGE. DESTRUCTION OF MOBILE HOMES ARE LIKELY!

Community Considerations Does your community building code set standards that will help buildings withstand winds in a major hurricane? Do your shelter facilities include long-span structures (such as gymnasiums) that are vulnerable in high winds? Do you have plans for post-storm tree clearance and temporary traffic control measures?

Tornadoes

Tornado damage from Hurricane Jeanne (2004) (mobile home, left) and Hurricane Frances (2004) (brick home, right) Tornadoes are one hazard from tropical cyclones that may catch many residents off-guard, especially since they are not usually accompanied by hail or a lot of lightning, clues that citizens often watch for. Although these tornadoes tend to be weaker and cause less damage than those spawned by other severe thunderstorms, it is important to make the public aware of this threat. About 4% of tropical cyclone deaths are caused by tornadoes. Almost all tropical cyclones that hit the U.S. spawn at least one tornado, and some develop multiple ones. For example, Hurricane Ivan (2004) produced a tornado outbreak of 127 tornadoes over several days, continuing after the storm crossed the Alabama coast. Historically, many other hurricanes have been known to be prolific tornado producers. Tornadoes can form with little or no warning, and we have no way at present to predict exactly which tropical cyclones will spawn tornadoes or where they will touch down. Doppler radar systems are the forecaster’s main warning tool, but the technology usually provides lead times from only a few minutes up to about an hour. Additionally, tornadoes can occur hundreds of miles from the center of a tropical cyclone. Consequently, preparedness and outreach is critical prior to the storm

Characteristics Tornadoes are embedded in a tropical cyclone’s rainbands; sometimes well away from the center of the storm. While more common on land, tornadoes can also occur at sea (called "waterspouts"), well before and sometimes hundreds of miles away from the eye of the storm. Additionally, tornadoes can develop as the remnants of a tropical cyclone travels inland and interacts with other weather features such as cold fronts.

Supercell thunderstorms (a type of storm that often forms tornadoes) embedded in Hurricane Ivan’s rainbands. At this time, (2104Z [4:04 pm CDT] on Sept. 15, 2004) the storms in the northern box were slowly dissipating, while the southern supercells were fully mature and continued generating tornadoes for several more hours. In general, the bigger and stronger the wind fields are with a tropical cyclone, the larger the favorable area for development of supercells and tornadoes. Recall from the discussion on structure (Basics section) that tornadoes usually occur in the right-front quadrant of the hurricane. Tornadoes can develop any time of the day or night, but by 12 hours after landfall, they tend to occur mainly during daytime hours.

Tornadoes are more likely to form in the right front quadrant of a hurricane

Damage Scale Like hurricanes, tornadoes are classified based on estimated wind speeds and the damage typically associated with each category. When a tornado occurs, trained NWS personnel assess the damage in comparison to a list of Damage Indicators – a table that describes various types of damage for different kinds of buildings (detailed table available at http://www.spc.noaa.gov/efscale/ef-scale.html). This table helps produce an estimate of the range of wind speeds the tornado likely produced.

Enhanced Fujita Tornado Damage Scale (Note: The Enhanced Fujita Tornado Damage Scale differs from the original Fujita scale in that it takes into account quality of construction and different types of structures and vegetation. Wind speeds are estimated from damage, not measured. Since damage can vary greatly from block to block or even building to building, rating tornadoes by the damage caused is subjective.)

Classification Estimated Winds (3 second gust) EF0

65-85 mph (105-137 km/h)

EF1

86-110 mph (138-178 km/h)

EF2

111-135 mph (179-218 km/h)

EF3

136-165 mph (219-266 km/h)

EF4

166-200 mph (267-322 km/h)

EF5

Over 200 mph (Over 322 km/h)

Most tornadoes spawned by tropical cyclones are relatively weak (EF0-EF1 based on the Enhanced Fujita Tornado Damage Scale), but a significant number have been EF2 or greater and have caused considerable damage.

Local Forecasts The best resources for keeping tabs on a tornado threat are NWS forecasts. The NWS Storm Prediction Center (www.spc.noaa.gov) analyzes the daily potential for tornadoes and severe thunderstorms. When conditions favor multiple tornadoes, the SPC will issue tornado watches for inland portions of tropical cyclones. The SPC is also responsible for severe weather outlooks and other forecast products that will discuss the potential for tornadoes. Local WFOs will also issue tornado watches and warnings based on local data and observations.

Tornado Watch: A watch is issued to alert the public that severe thunderstorms and tornadoes are possible during the next few hours, in and around the watch area. A tornado watch does not mean that tornadoes will occur, only that they are possible. Tornado Warning: A warning means that a tornado has been sighted by storm spotters or has been indicated by radar. These warnings are issued with information concerning where the tornado is presently located and what communities are in the anticipated path.

Below is an example of a tornado warning and watch statement:

TORNADO WARNING BULLETIN – EAS ACTIVATION REQUESTED TORNADO WARNING

NATIONAL WEATHER SERVICE MOBILE AL 1205 PM CENTRAL DAYLIGHT TIME MON SEP 1 2008 THE NATIONAL WEATHER SERVICE IN MOBILE HAS ISSUED A TORNADO WARNING FOR, SOUTHERN OKALOOSA COUNTY IN NORTHWEST FLORIDA, THIS INCLUDES THE CITIES OF, FORT WALTON BEACH, DESTIN, UNTIL 1245 PM CENTRAL DAYLIGHT TIME.

AT 1202 PM CENTRAL DAYLIGHT TIME, THE NATIONAL WEATHER SERVICE INDICATED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO 9 MILES SOUTHEAST OF DESTIN, MOVING NORTHWEST AT 41 MPH. THE TORNADO WILL BE NEAR,DESTIN BY 1215 PM CENTRAL DAYLIGHT TIME,EGLIN AFB BY 1220 PM CENTRAL DAYLIGHT TIME,

THE SAFEST PLACE TO BE DURING A TORNADO IS ON THE LOWEST FLOOR OF A STURDY BUILDING, PREFERABLY IN AN INTERIOR HALLWAY OR A ROOM SUCH AS A CLOSET OR BATHROOM. IF POSSIBLE, GET UNDER A WORKBENCH OR OTHER PIECE OF STURDY FURNITURE. USE BLANKETS OR PILLOWS TO COVER YOUR BODY AND ALWAYS STAY AWAY FROM WINDOWS. IN ADDITION TO THE TORNADO, THIS STORM IS CAPABLE OF PRODUCING LARGE DAMAGING HAIL OR DAMAGING STRAIGHT LINE WINDS.

IF YOU ARE IN MOBILE HOME, EVACUATE IT AND GET ON THE LOWEST FLOOR OF A NEARBY STURDY BUILDING OR IN AN UNDERGROUND STORM SHELTER. IF NO SUBSTANTIAL SHELTER IS AVAILABLE AND A TORNADO IS FAST APPROACHING, SEEK SHELTER IN A CULVERT, DITCH OR LOW DEPRESSION AND COVER YOUR HEAD WITH YOUR HANDS.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 400 PM CENTRAL DAYLIGHT TIME MONDAY AFTERNOON FOR SOUTHWESTERN ALABAMA AND NORTHWEST FLORIDA AND SOUTHEAST MISSISSIPPI.

The possibility for tornadoes may also be mentioned in the HLS, as in this example:

.SITUATION OVERVIEW... CLAUDETTE HAS TAKEN A WESTWARD JOG AND WILL KEEP THE MAIN WIND IMPACTS SOUTH OF THE FORECAST AREA. HOWEVER...GUSTY WINDS MAY CAUSE SOME WEAK TREES TO FALL AND POWER LINES MAY BE AFFECTED. HEAVY RAIN BANDS WILL BE POSSIBLE FROM 1 TO 3 INCHES ACROSS THE AREA. ISOLATED LOCALIZED FLOODING IS POSSIBLE. ISOLATED WEAK TORNADOES ARE ALSO POSSIBLE IN THE NORTH AND EAST OUTER BANDS WELL AHEAD OF THE STORM.

Community Considerations Do residents of your community know where to go if threatened by a tornado?

Questions Question 1 In general, most deaths from tropical cyclones that have moved inland occur as a result of: (Choose the best answer) k

a) Tornadoes b) High winds k c) Storm surge k d) Heavy rainfall

The correct answer is d. Flooding from heavy rainfall has caused most hurricane-related deaths in inland areas.

Question 2 On the coast, most deaths from tropical cyclones usually occur from: (Choose the best answer) ka) Tornadoes

b) High winds c) Storm surge kd) Heavy rainfall

The correct answer is c. In coastal areas, storm surge is the most dangerous hazard, which is why those areas are usually the first to be evacuated.

Question 3 Other things being equal, storm surge will be greater in an area where the continental slope is shallow. n

a) True b) False

The correct answer is True.

In general, a shallow continental slope offshore of a coast will result in a larger storm surge than a steep continental slope.

Question 4 If a hurricane is predicted to have a storm surge of 9 feet, and the storm will come ashore during a low tide of 1.0 ft, which locations on the coast would likely be affected? (Choose the best answer) kn kn kn kn

a) Places at elevations lower than 8 feet b) Places at elevations lower than 9 feet c) Places at elevations lower than 10 feet d) Places at elevations higher than 10 feet

The correct answer is c. In order to calculate the total storm tide, add the storm surge (9 ft) and the tide value (1 ft). Areas at elevations less than that are at risk of flooding from storm surge.

Question 5 Winds at the top of a high rise building are usually: (Choose the best answer)

n

a) Faster than the winds at ground level b) Slower than the winds at ground level c) About the same speed as the winds at ground level d) From a different direction than the winds at ground level

The correct answer is a. Wind speeds usually increase with height above ground level, so the winds at the top of a high rise building can be expected to be stronger than those at ground level.

Question 6 Flooding is more likely when: (Choose all that apply)

g g g

a) A storm is moving 15 mph or more b) Heavy rains have occurred recently c) A storm is over flat terrain d) A storm is large

g

e) Bands of rain stay over the same location

The correct answers are b, d, and e. Flooding is more likely if previous rain has already saturated the ground, the tropical storm is large so the rains cover a larger area, and if the rainbands move slowly. Also, flooding is more likely in hilly/mountainous areas where the streams are more confined and cannot spread out.

Question 7 Which statement(s) about the graphic below is (are) correct? (Choose all that apply)

g

a) At the current time, the river height is about 27.2 feet g b) The river is predicted to result in a major flood g c) At the end of the forecast period, the flood expected to be over g d) At its peak, the river is expected to be about 14 feet above its lowest level on Nov. 18

The correct answers are b and d. The green dotted line indicates that the river is expected to crest at 27.2 ft, which is just slightly above what is considered Major Stage (27.0 ft, indicated by the purple area). At the current time (the black dashed line), the

level is 26.45 ft. The lowest level in the 10 days depicted in the graph is about 13 ft (blue line), so 27.2-13 ft is just slightly more than 14 ft above the lowest level during the week.

Question 8 Evacuations should be complete by the time winds reach Saffir-Simpson Category 2. n n

a) True b) False

The correct answer is False. The rule of thumb is that evacuations should be complete when winds reach tropical storm force speed (39-73 mph or 34-63 kt). This is because winds at these speeds can blow hazardous debris around, jeopardizing the safety of the public and emergency responders.

Question 9 The right-front quadrant of a hurricane is important because: (Choose all that apply) g

a) Most of the precipitation falls in this area b) Tornadoes are more likely to occur here g c) Storm surge is usually greater in this area d) Wind speeds are greatest in this area g e) The storm moves slowest in this area g

g

The correct answers are b, c, and d. Recall from the Basics section that the steering winds compound the hurricane wind speeds in the right-front quadrant. That additional wind speed also creates higher storm surge in this area (other factors, such as continental slope, being equal). Tornadoes also are more likely to occur in this part of the storm.

Question 10 A tornado warning means that a tornado is possible sometime in the next few hours. n n

a) True b) False

The correct answer is False.

A warning means that a tornado has been sighted by observers or that radar shows that one has probably formed, and that people in the affected areas should take appropriate shelter immediately. A watch means that conditions are right for tornado formation and that people should be alert and should monitor NOAA weather radio and media broadcasts.

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