U NDERSTANDING H URRICANES A ND T HEIR H AZARDS Kennard “Chip” Kasper Senior Forecaster NOAA/National Weather Service Key West, Florida June 26, 2011 Marathon City Marina

Points of Genesis (Tropical Storms and Hurricanes) (Atlantic) (Pacific)

U NDERSTANDING H URRICANES A ND T HEIR H AZARDS I.Hurricanes: The Basics Terms/definition Structure Ingredients for formation Frequency Prediction II.Hurricane Hazards Wind, Surge, Tornadoes, Rain

T HE B ASICS HURRICANE: A tropical cyclone in which the maximum sustained surface wind (1-minute average) is 74 mph or more. TROPICAL CYCLONE: A warm-core non-frontal cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center. Once formed, a tropical cyclone is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere. In this they differ from extratropical cyclones, which derive their energy from horizontal temperature contrasts in the atmosphere. U NDERSTANDING H URRICANES A ND T HEIR H AZARDS

EYESPIRAL RAINBANDS EYEWALL

Beaufort Knots Description Number 0 < 1 Calm Light air Light breeze Gentle breeze Moderate breeze Fresh breeze Strong breeze Near gale Gale Strong gale Storm Violent storm 12 > 63 Hurricane The Beaufort Scale

The Saffir-Simpson Hurricane Intensity Scale Category Wind Speed (mph)

H URRICANE G ENESIS: I NGREDIENTS 1. Warm ocean water (at least 80 o F) 2. Atmosphere that cools fast enough with increasing height 3. Relatively moist layers in the middle troposphere 4. A pre-existing near-surface disturbance with sufficient “spin” 5. Low values of vertical wind shear between the surface and upper troposphere U NDERSTANDING H URRICANES A ND T HEIR H AZARDS

Large FLOYD (1999) Small ANDREW (1992) Variability in Hurricane Size

Tropical cyclone tracks, Where do tropical cyclones occur? FL Keys

Atlantic Ocean Gulf of Mexico Caribbean Sea FL

Chance of a named tropical cyclone within 100 miles of a given location During the hurricane season (June 1 – November 30). Based on years Figure courtesy of Todd Kimberlain. Marathon: ~ 47%

Chance of a hurricane within 100 miles of a given location during the hurricane season (June 1 – November 30). Based on years Figure courtesy of Todd Kimberlain. Marathon: ~ 17%

Chance of a major hurricane (category 3, 4, or 5) within 100 miles of a given location during the hurricane season (June 1 – November 30). Based on years Figure courtesy of Todd Kimberlain. Marathon: ~ 5 %

ALL HURRICANES –

H URRICANE D ONNA -- S EPTEMBER 10, Category 4 hurricane - Maximum 1-minute average wind of 147 mph recorded at Sombrero Key Lighthouse - Storm surge 8 to 14 feet through portions of the Middle and Upper Keys - Few lives were lost due to low population density and timely evacuations - Severe destruction in Middle/Upper Keys - Aqueduct severed in 3 places - Roads/bridges washed out between Marathon and Islamorada - Damage in Key West was light; however, no water, no communications, and no access to mainland by road for 3 months!

T ROPICAL C YCLONE P REDICTION MONITORING PHASE: Daily observation and analysis of the atmosphere and ocean in tropical cyclone genesis regions. Daily issuance of Tropical and Hazardous Weather Outlooks and Area Forecast Discussions. Low predictability; high uncertainty. EVENT IMPACT WARNING PHASE: WATCH PHASE: Tropical cyclone has developed and threatens the coast; Watch issued for TC conditions possible within 48 hours. Tropical cyclone moving toward coast; Warning issued for TC conditions within 36 hours IN THE KEYS, NON-RESIDENT EVACUATIONS BEGIN ABOUT 72 HOURS BEFORE EXPECTED IMPACT MANDATORY RESIDENT EVACUTATIONS FOR CATEGORY 3, 4, 5 STORMS BEGIN AT 48 HOURS BEFORE EXPECTED IMPACT

T ROPICAL C YCLONE T RACK F ORECASTS Forecast Hour Error (miles)

T ROPICAL C YCLONE I NTENSITY F ORECASTS Forecast Hour Error (MPH)

Mean Atlantic Basin Tropical Cyclone Track Error Rings ( ) Referenced to Marathon, Florida Radii correspond to forecast projections of 24, 48, 72, 96, and 120 h Forecast Projection Mean Track Error # Forecast Projection Mean Error % # statute miles % knots

The Saffir-Simpson Hurricane Intensity Scale Category Wind Speed (mph)

H URRICANE H AZARDS STORM SURGE WIND TORNADOES/ WATERSPOUTS “INLAND” FLOODING

STORM SURGE In general, An abnormal rise of water generated by a storm, over and above the predicted astronomical tides.

STORM SURGE PREDICTION In a hurricane, actual high water marks at a particular location depend on many factors: - Storm intensity (pressure/wind/wave forces) - Storm structure (size of storm/radius of maximum winds) - Storm movement (track with respect to your location; also forward speed) - Coastal bathymetry (underwater topography) - Ground elevation In general, Successful storm surge predictions require accurate forecasts of storm intensity, storm structure, and storm movement, plus reliable bathymetry and ground elevation data!

SLOSH (Sea, Lake, and Overland Surges from Hurricanes) Computerized model run by the National Hurricane Center to estimate storm surge heights and winds resulting from historical, hypothetical, or predicted hurricanes by taking into account: Pressure Size Forward Speed Track Winds Graphical output from the model displays color coded storm surge heights for a particular area in feet above a reference level. Calculations are applied to a specific locale’s shoreliine, incorporating the unique bay and river configurations, water depths, bridges, roads, and other physical features.

SLOSH (Sea, Lake, and Overland Surges from Hurricanes) Generally accurate within plus or minus 20 percent (provided that meteorological inputs are accurate!) Where the hurricane forecast track is inaccurate, SLOSH model results will be in accurate. The SLOSH model, therefore, is best used for defining the potential maximum surge for a location. Basis for “hazard analysis” portion of coastal hurricane evacuation plans

Wave Set-Up Adds to Storm Surge and is NOT calculated by SLOSH! Inside the Reef, breaking waves can pile up 3 to 5 feet of water…IN ADDITION TO THE SLOSH-CALCULATED STORM SURGE…in a category 5 hurricane in the Florida Keys. This is because the strong winds blowing over shallow water do not permit the water to return to the deeper ocean. Wave Set-Up can add several feet to a SLOSH-calculated storm surge. All other things being equal, the Reef actually can make storm surge flooding WORSE in the Keys! For example, SLOSH predicts the maximum category 5 surge in southern Stock Island to be about 12 ½ feet. 5 feet of runup could bring the storm tide to 17 ½ feet !!!

Storm Surge Exceedance products will become operational in The exceedance graphics show the storm surge height, in feet above normal tide level, which has a specific probability of being exceeded in the next 3 days. The available probability thresholds range from 10 to 90 percent, at 10 percent intervals. The products are available on the NHC website when a hurricane watch or warning is in effect for the United States. Information on NHC Storm Surge products is found at: Probabilistic Storm Surge

Tornadoes Associated with Tropical Storms and Hurricanes in the Florida Keys All Florida Keys TC tornadoes: TC tornadoes / 13 TCs 35% of total (65) 61% associated with TS or TD

A Climatology of Tropical Cyclone-Induced Tornadoes in the Florida Keys Map of the Florida Keys with names and locations of communities affected by tropical cyclone tornadoes.

A Climatology of Tropical Cyclone-Induced Tornadoes in the Florida Keys Mean sea level pressure composite analysis for Florida Keys tropical cyclone tornadoes using six-hourly NCEP/NCAR reanalysis data; image provided by NOAA/ESRL Physical Sciences Division, Boulder, Colorado from their web site at

A Climatology of Tropical Cyclone-Induced Tornadoes in the Florida Keys Tracks of tropical cyclones associated with tornadoes in the Florida Keys, Image courtesy of NOAA Coastal Services Center. 62% of TCs originated over Western Caribbean 23% Cape Verde storms 15% developed in vicinity of Greater Antilles

A Climatology of Tropical Cyclone-Induced Tornadoes in the Florida Keys

Tropical Storm Agnes Tornado Outbreak At least 3 (possibly up to 6) tornadoes EST 2 F2 tornadoes 40 injuries / $500,000 (1972 dollars) Trailer parks hit hard Early season tropical storm Acknowledgments: Bart Hagemeyer

QUESTIONS??? F OR M ORE I NFORMATION : Internet: Address: 1315 White Street Key West, FL