Kelly Godsey and Jeffry Evans National Weather Service Tallahassee, Florida

Kelly Godsey and Jeffry EvansNational Weather Service

Tallahassee, Florida

Basic Tropical DefinitionsTropical Depression: A tropical cyclone that has

maximum sustained winds 38 mph or less. Tropical Storm: A tropical cyclone that has

maximum sustained winds between 39 mph and 73 mph.

Hurricane: A tropical cyclone that has maximum sustained winds of 74 mph or greater.

Major Hurricane: A tropical cyclone that has maximum stained winds of 111 mph or greater.

Saffir-Simpson Hurricane Scale: The rating system for hurricanes based on maximum wind speed.

Saffir-Simpson Hurricane Wind ScaleCategory Wind Speed Range

(peak 1-minute wind)

1 74-95

2 96-110

3 111-130

4 131-155

5 156-??

Extratropical storm (1993)

Subtropical Storm Gustav (2002)

Hurricane Rita (2005)

Three types of Cyclones

Tropical and Extratropical Storms

Structure of a Tropical CycloneFeeder Bands

Feeder Bands

Central Dense Overcast

Eye

Cross Section of a Hurricane

What the Hurricane Hunters Saw in Katrina

What drives tropical cyclones?Tropical systems are steered by the upper

level windsTypically, the Bermuda High and it’s location

will determine how large hurricanes move across the Atlantic.

An approaching trough of low pressure can cause a system to “recurve” before reaching the United States

Simulation

What is required for tropical cyclones to form?

Lots of moisture

Low wind shear

Sufficently deep warm ocean water

Where do we look for tropical cyclone formationIt all depends on the time of the year and if

the ingredients for development existTropical systems typically form in the

Caribbean or Gulf of Mexico at the beginning and end of the season.

Development shifts to the Central and Eastern Atlantic in the middle of the season.

Development in June

Development in July

Development in August

Development in September

Development in October

Development in November

ClimatologyCompared to the rest of Florida, hurricane

landfalls in the Florida Big Bend are rare. Landfalls in the Florida Panhandle are higher over the last 100 years.

Storm Names – Where did they come from?

Prior to 1953 meteorologists informally named tropical systems to keep track of multiple active storms.

Starting in 1953, a list using only female names was introduced.

In 1970, Grandpa Jones explains why only female names were used at first.

Storm Names – ContinuedMen’s names joined the list in 1979Six lists are used and rotate each seasonStorms that are especially deadly or cause

significant damage are permanently retired from the active list.

Katrina, Hugo, and Andrew are notable examples.

In the event all storm names are used for a single hurricane season, the Greek Alphabet is used: Alpha, Beta, Gamma, Delta, etc.

2010 Storm NamesAlex Bonnie

Colin Danielle

Earl Fiona

Gaston Hermine

Igor Julia

Karl Lisa

Matthew Nicole

Otto Paula

Richard Shary

Tomas Virginie

Walter

Replacement name (2004)

Important changes for the 2010 Hurricane SeasonHurricane/Tropical Storm Watches now mean

conditions are possible within 48 hours. Hurricane/Tropical Storm Warnings now mean

conditions are expected within 36 hours. The Public Advisory format has changed. Saffir-Simpson Scale no longer tied to storm

surgeNew Coastal Zones for Tallahassee Forecast

AreaOur pre-season hurricane guide, complete with

these changes and more will be available by the last week of April.

Why change the watch/warning timesTrack errors at 48 hours are now similar to

those years ago at 36 hours. Greater lead time is needed to evacuate some

coastal counties.What does this mean?

Watches may be posted as much as 3 days prior to arrival of the predicted condition, especially for larger storms.

New Public AdvisoryInstead of paragraph format, product divided

into five sections to provide better access to informationSummary of storm locationWatches and Warning Summary

New watches and warning changes first Summary to follow

Discussion and 48 hour outlookHazards affecting land (surge, wind, rainfall

etc.) Next advisory time

Observed Storm Surge Different from that Advertised by Saffir-Simpson Hurricane Scale

storm surge is modulated by more than justthe peak wind

IKE (2)

CHARLEY (4)

New Coastal Zones for NWS Tallahassee

Coastal Zones and HurricanesCoastal zones were designed based on storm

surge climatology and other coastal effects. Coastal zones will carry any tropical storm or

hurricane watches and warningsInland zones in coastal counties and inland

counties will carry tropical storm or hurricane wind watches and warnings.

Seasonal Forecast FactorsStatus of El Nino Southern OscillationAtlantic Sea Surface Temperature

observations relative to normal. Rainfall occurring over Sub-Saharan Africa Prevailing atmospheric conditions over North

America

El Nino Status

Latest forecasts for the 2010 SeasonOrganization Tropical

StormsHurricanes Major

Hurricanes

Colorado State (Dec ‘09)

11-16 6-8 3-5

Colorado State (Apr ‘10)

15 8 4

NOAA (due May ‘10) ?? ?? ??

Normal Values (1970-2010)

10 6 2

2009 Hurricane Season

9 3 2

**Seasonal forecasts are to be considered only as a guide. 1995 began a period of above normal activity. Only three seasons since 1995 have featured below normal activity in the Atlantic Basin.

Watching for a storm to developThe National Hurricane Center continually monitors the tropical Atlantic for signs of development. Four times a day, NHC issues a text and graphical tropical weather outlook.

• Issued at 8 am, 2 pm, 8 am, and 2 am Eastern Time.

•This outlook highlights areas at increased risk for development.

• The graphical map includes a “mouse over” ability

• Active tropical systems are indicated on the map.

A storm Develops in the Atlantic• The initial development is called a tropical depression. • When winds reach 39 mph, the depression will receive a name and be called a tropical storm. • When winds reach 74 mph, the storm becomes a hurricane

NHC Website for active storms• NHC is responsible for issuing advisories on tropical systems.

• Website includes sections devoted to each active storm.

• Text products include:

• Public Advisory

• Forecast/Advisory

• Forecast Discussion

• Wind Speed Probabilities

• Graphics are provided in the section below.

• Sample

What are the wind speed probability graphics?

Display the percentage 34 knot, 50 knot, or 64 knot winds are possible in your location over the next five days, or 120 hours.

Corresponds with a text version that provides details for the onset of 34 knot, 50 knot, or 64 knot winds. Example

Text Probability TableIssued by NHC with each advisory packageDetails probability of 34kt, 50kt, and 64kt

winds during a particular interval and throughout the entire 5 day forecast period.

Well known locations chosen in the projected area of impact

Sample Interval and Cumulative Probability Product

Terms of UncertaintyUtilizes the probability

data provided by the National Hurricane Center in conjunction with the forecast prepared by local meteorologists.

Available through the point and click forecast accessible from the Tallahassee main page.

Includes both graphics and text

Terms of Uncertainty (Con’t)

Wednesday

Wednesday Night

Thursday

• There are six phrases that can be used:

• Tropical Storm (Hurricane) conditions possible: This phrase will be used most often.

• Tropical Storm (Hurricane) conditions expected: This phrase requires a watch or warning to be in effect with a high degree of confidence

•Tropical Storm (Hurricane) Conditions: This phrase is only used in the first 24 hours of the forecast.

Storm Impacts for our Region

Storm Surge Defined

STORM SURGE is an abnormal rise of water generated by a storm, over and above the predicted astronomical tide.

STORM TIDE is the total water level during a storm (i.e astronomical tide + storm surge)

Storm Surge/Storm Tide

DEEP WATER

b. Side view of Cross Section “ABC”a. Top view of Sea Surface

0’

5O’

100

’

150

’

200

’

Wind

Current

A B CMSL

A B

Eye

CWind

LANDFALL

b. Side view of Cross Section “ABC”a. Top view of sea surface and land

Wind

A B C0’

50’

100

’

150

’

200

’

Continental ShelfBarrierIsland

Mainland

A B C

Eye

Current

MSL

STORM SURGE

Wind

STORM SURGE

Width and Slope of ShelfWide shelf/ gentle slope

Narrow shelf/ sharp slope

Start of shelf trapped waveup the Florida Coast

180 miles

Storm Surge and the NWSNational Hurricane Center provides forecasts

for all tropical cyclones in the Atlantic Basin. When a hurricane watch is issued for any

portion of the U.S. Coast, NHC begins operational runs for the active system based on the latest forecast track.

Probabilistic surge runs are also available, which take into account forecast uncertainty.

Alternative to Single RunsAtlas of pre-computed surge maps based

on:Different directions of motionDifferent landfall locationsDifferent intensitiesDifferent storm sizesDifferent forward speeds

Available Ensemble Products

MEOWs

MOMs

Probabilistic

• Maximum Envelope of Water• Composite of maximum storm surge heights at

each grid cell using hypothetical hurricanes run with the same:

– Category (Intensity)– Forward Speed– Landfall Direction– Initial Tide Levels

• Composite achieved by reviewing parallel tracks that make landfall at different locations

• Over 80 MEOWs have been generated for some basins

MEOW

• Maximum of MEOWs• Composite of the maximum

storm surge height for all hurricanes of a given category

• Disregards forward speed, landfall direction, landfall location, etc.

• Only 5 MOMs per basin, i.e. one per storm category

MOM

Probabilistic Storm Surge

Use an ensemble of SLOSH runs to create probabilistic storm surge(p-surge)

Intended to be used operationally so it is based on NHC’s official advisory

P-surge’s ensemble perturbations are determined by statistics of past performance of the advisories

P-surge uses a representative storm for each portion of the error distribution space rather than a random sampling

Errors Used by P-surge

The ensemble is based on distributions of the following:

Cross track error (impacts Location)

Along track error (impacts Forward Speed, Timing)

Intensity error (impacts Pressure)

Rmax error (impacts Size)

Example: Cross Track Error

Understanding/Using Probability

•The number one argument against using probability is that users do not understand how to interpret low probabilities of an extreme event

•The odds of winning the Mega Millions lottery are 1 in 135,145,920, yet ~1/2 of Americans play the lottery (AP)

Surge Guidance Timeframe

Day 5: MOMs

Day 4: MEOWs/MOMs

Day 3: MEOWs/MOMs

Day 2: MEOWs/P-Surge/Operational Runs

Day 1: MEOWs/P-Surge/Operational RunsGiven current NHC intensity errors, always allow

for one category higher on the Saffir-Simpson scale

Don’t forget about the Tornadoes!

• Tornadoes are possible with any landfalling tropical system.

• Tornadoes are likely in the right front quadrant of the storm.

• It is difficult to predict how great the risk of tornadoes will be with an individual tropical system.

• Hurricane Ivan (at right), produced a considerable number of tornadoes.

• Hurricane Dennis was not a prolific tornado producer

Right front quadrant

Tornadoes with hurricanes Just over ½ of land-falling hurricanes

produce tornadoes. These are generally EF0-EF2. Occur without hail and often with

no lightning. Develop anytime, day or night

Some factors found favorable: ‘Dry’ air at the mid levels of

atmosphere drawn into system. Accelerating and/or strengthening

systems at land-fall. Tornado threat can linger for days and

can both increase and become more associated with aftn heating 12+ hrs post-land. Could see an extended period under

tornado watches.

9/15/04

9/16/04

9/17/04

IVAN

Ivan (2004) tornadoes24 tornadoes

were reported in our forecast area

117 tornadoes were reported across the Southeast

Six fatalities occurred in our region

In addition to numerous hazards with major hurricane!

Tools Available LocallyHurricane Local Statement

Text description of storm surge impactsGraphical Hurricane Local Statement

Images detailing storm surge impact for each county.

Overview section of the Hurricane Local Statement

Hurricane Local Statement Segments

• Segment 1 is focusing on threats for portions of South Central Georgia

• Segment 2 is focusing on the Southeast Florida Big Bend. Specific information regarding storm surge will be included here.

Graphical Hurricane Local StatementDesigned to provide a quick look at the risk

level from all hazards in a tropical system.NWS Tallahassee uses five tiered ranking

system for assigning risk. (None, Low, Moderate, High, Extreme)

Maps available for Wind, Inland Flooding, Surge, and Tornadoes.

Product is only active when Tropical Storm or Hurricane watches or warnings are in effect for our region.

Mouse over capability to display HLS text

Can show higher impacts at the coast.

GHLS-NWS Tallahassee

WebinarsNWS Tallahassee conducts webinars when a

tropical system will potentially pose a threat to our area.

Webinars are designed for the emergency management community.

Emergency management groups may invite media partners to their EOCs to view the presentation as a method of increasing public awareness of significant weather events.

Webinars for tropical events will typically be held at 930 am ET or 230 pm ET

Feedback from youWe are interested in your thoughts on our

performance. What is one area that we can improve?What is something we aren’t doing that you’d

like us to do?

Questions? Comments?Thank you for coming to our emergency

management training day. We are having an afternoon session on Hurrevac 2010 that you are more than welcome to stay for.