Presentation on theme: "NOAA National Weather Service Baltimore/Washington Forecast Office"— Presentation transcript:
1NOAA National Weather Service Baltimore/Washington Forecast Office Marine Weather CourseNOAA National Weather ServiceBaltimore/Washington Forecast Office
2Part I Outline National Weather Service Introduction Baltimore/Washington Forecast Office Operations and Marine AreaKey Marine Products and HazardsMarine Observation and Forecast InformationMarine SafetyMarine Reporting
4WFO Area of Responsibility Region is prone to all weather hazardsMaryland13 CountiesCity of BaltimoreWest Virginia8 CountiesVirginia22 Counties11 independent citiesDistrict of ColumbiaRiver BasinsPotomacShenandoahRappahannockMarine AreaTidal Potomac RiverMD Chesapeake BayApproximately 27,000 square miles Serving ~9 Million People
5Operations & Services Convective - Tornado & Severe Thunderstorm Spruce Knob,Pendleton County, WVElevation 4,861 feetConvective- Tornado & Severe ThunderstormTropical Systems- Hurricanes & Tropical StormsNon-Precipitable- Heat Waves- High Wind- Wind Chill/Excessive ColdHydrological- Flash Floods- River Floods- Small Stream & TributariesWinter StormsCoastal FloodingWildfire (Red Flag)
9Coastal Waters Forecast Issued a minimum of 4 times / dayAmendments issued as necessaryEach CWF goes out 5 days, with each period covering 12 hoursUsed by small pleasure boaters to large commercial transport ships.
10Coastal Waters Forecast Elements:Synopsis – Short, conciseHeadlines of long duration hazards: Advisories, Watches, WarningsWind – from 8 compass points, in knots (kt)Waves – wave heights, in feet (ft)Weather – thunderstorms, rain, snow and fog (significant visibility reduction)
11Long Duration HazardsSmall Craft Advisory: (Tidal Potomac and Chesapeake Bay) -- the following conditions are occurring or expected to begin within the first 3 forecast periods:Sustained winds ktFrequent gusts kt(frequent refers to lasting > 2 hours)Waves 4 ft
12Long Duration HazardsGale Warning: (Tidal Potomac and Chesapeake Bay) -- the following conditions are occurring or expected to begin within the first 3 forecast periods:Sustained winds ktFrequent gusts kt
13Long Duration HazardsStorm Warning: (Tidal Potomac and Chesapeake Bay) -- the following conditions are occurring or expected to begin within the first 3 forecast periods:Sustained winds ktFrequent gusts kt
14Long Duration HazardsHurricane Force Wind Warning: (Tidal Potomac and Chesapeake Bay) -- the following conditions are occurring or expected to begin within the first 3 forecast periods:Sustained winds 64 kt or greaterFrequent gusts 64 kt or greaterNot associated with a tropical system
15Tropical Hazards Tropical Watches/Warnings Initiated by National Hurricane Center in Miaminhc.noaa.govTropical Storm (sustained winds 34 to 63 kt / 39 to 73 mph)Hurricane (sustained winds > 64 kt / > 74 mph)Isabel, 2003
16Convective Hazards Severe Local Storm Watches Initiated by Storm Prediction Center in Norman, OKspc.noaa.govTornado WatchSevere Thunderstorm Watch
17Coastal Waters Forecast ANZ/X.EXT.KLWX.SC.Y T1200Z T2200Z/TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD-TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND-337 AM EDT SUN OCT...SMALL CRAFT ADVISORY NOW IN EFFECT FROM 6 AM EDT THIS MORNING THROUGH THIS AFTERNOON....TODAY...NW WINDS 15 TO 20 KT. WAVES 1 TO 2 FT..TONIGHT...E WINDS 5 TO 10 KT. WAVES 1 FT OR LESS..MON...NE WINDS 5 TO 10 KT. WAVES 1 FT OR LESS. A CHANCE OFSHOWERS..MON NIGHT...N WINDS 10 TO 15 KT. WAVES 1 FT. A CHANCE OF SHOWERS..TUE...NW WINDS 15 TO 20 KT. WAVES 1 TO 2 FT..TUE NIGHT...NW WINDS 10 TO 15 KT. WAVES 1 FT..WED...W WINDS 10 TO 15 KT. WAVES 1 FT..THU...NW WINDS 5 TO 10 KT. WAVES 1 FT OR LESS.$$
18Special Marine Warnings Issued for potentially hazardous over-water weather conditions of short duration (2 hours or less) and producing winds speeds or gusts 34 kt or greater not covered by existing longer fused products.Gusty showers/thunderstorms with winds 34 kt or greaterWaterspouts
19Special Marine Warnings BULLETIN - IMMEDIATE BROADCAST REQUESTEDSPECIAL MARINE WARNINGNATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC621 PM EST SUN NOVTHE NATIONAL WEATHER SERVICE IN STERLING VIRGINIA HAS ISSUED A* SPECIAL MARINE WARNING FOR...CHESAPEAKE BAY NORTH OF POOLES ISLAND, MD...CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT, MD...* UNTIL 745 PM EST* AT 621 PM EST...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A CLUSTER OF GUSTY SHOWERS ABOUT 20 MILES WEST OF BALTIMORE HARBOR.... MOVING EAST AT 45 MPH. IN ADDITION...GUSTY WINDS ASSOCIATED WITH A COLD FRONT WILL PASS OVER THE WATERS JUST AFTER THE SHOWERS PASS THROUGH AFTER 7 PM.* THIS ACTIVITY WILL AFFECT THE WATERS AFFECT...BALTIMORE INNER HARBOR...HART MILLER ISLAND...POOLES ISLAND...TOLCHESTER BEACH...MARINERS CAN EXPECT WIND GUSTS OVER 35 KT...HIGH WAVES...LIGHTNING AND HEAVY DOWNPOURS. BOATERS SHOULDSEEK SAFE HARBOR IMMEDIATELY UNTIL THIS STORM PASSES.LAT...LON$$
20Marine Weather Statements Update/Continue Special Marine WarningExpire/Cancel Special Marine WarningIssued for long term sub-severe hazards lasting for longer than 2 hours that will impact marine operations
21Marine Weather Statements NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC1045 AM EDT SUN AUGANZ/O.CON.KLWX.MA.W T0000Z T1545Z/...A SPECIAL MARINE WARNING CONTINUES UNTIL 1145 AM EDT...FOR THE FOLLOWING AREA...CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT, MDAT 1044 AM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO INDICATE A LINE OF THUNDERSTORMS...PRODUCING STRONG WINDS OVER 35 KNOTS FROM CEDAR BEACH TO 9 MILES SOUTHWEST OF ROCK HALL...OR FROM 7 MILES WEST OF POOLES ISLAND TO 3 MILES NORTH OF SANDY POINT...MOVING NORTHEAST AT 15 MPH.OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO HART MILLER ISLAND...CARROLL ISLAND...TOLCHESTER BEACH AND ROCKY POINT.MARINERS CAN EXPECT GUSTY WINDS...HIGH WAVES...REDUCED VISIBILITIES...DANGEROUS LIGHTNING...AND HEAVY RAINS. BOATERS SHOULD SEEK SAFE HARBOR IMMEDIATELY...UNTIL THIS STORM PASSES.FREQUENT LIGHTNING IS OCCURRING WITH THIS STORM. IF CAUGHT ON THE OPEN WATER STAY BELOW DECK IF POSSIBLE...KEEP AWAY FROM UNGROUNDED METAL OBJECTS.$$
22NowcastsIssued for short term non-severe hazards but potentially dangerous conditions, such as with winds to 33 kt lasting for 2 hours or less.Sometimes combined with land zones, but oftentimes appearing only as a marine Nowcast.
23Nowcasts SHORT TERM FORECAST NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC804 AM EDT FRI OCTANZ530>537-DCZ001-MDZ005> > >018-VAZ >ANNE ARUNDEL MD-ARLINGTON/FALLS CHURCH/ALEXANDRIA VA-CALVERT MD-CARROLL MD-CHARLES MD-DISTRICT OFCOLUMBIA DC-FAIRFAX VA-FAUQUIER VA-HARFORD MD-HOWARD MD-KING GEORGE VA-LOUDOUN VA-MONTGOMERY MD-NORTHERN BALTIMORE MD-PRINCE GEORGES MD-PRINCE WILLIAM/MANASSAS/MANASSAS PARK VA-SOUTHERNBALTIMORE MD-SPOTSYLVANIA VA-ST.MARYS MD-STAFFORD VA-CHESAPEAKE BAY FROM DRUM POINT, MD TO SMITH POINT, VA-CHESAPEAKE BAY FROM NORTH BEACH TO DRUM POINT, MD-CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT, MD-CHESAPEAKE BAY FROM SANDY POINT TO NORTH BEACH, MD-CHESAPEAKE BAY NORTH OF POOLES ISLAND, MD-TIDAL POTOMAC FROM COBB ISLAND, MD TO SMITH POINT, VA-TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND, MD-TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD, MD-.NOW......HEAVY RAIN AND THUNDERSTORMS AFFECTING THE MORNING COMMUTE...AT 804 AM EDT...DOPPLER RADAR INDICATED A LINE OF HEAVY RAIN WITH EMBEDDED THUNDERSTORMS...LOCATED FROM JUST WEST OF BALTIMORE TO JUST WEST OF WASHINGTON DC AND FURTHER TO THE SOUTH. THIS ACTIVITY WAS MOVING EAST AT 25 MPH.MORNING COMMUTERS SHOULD EXPECT TO ENCOUNTER BRIEF HEAVY RAIN...GUSTY WINDS UP TO 30 MPH...AS WELL AS LIGHTNING. SOME OTHER COMMUNITIES THAT WILL SEE THIS ACTIVITY THROUGH 930 AM INCLUDE LAUREL BROOK...SCARFF...BELLEVIEW...WOODBRIDGE...FALLSTON.THE TIDAL POTOMAC AND CHESAPEAKE BAY COASTAL WATERS WILL ALSO EXPERIENCE THIS ACTIVITY AFTER 830 AM. MARINERS SHOULD ANTICIPATE THE GUSTY WINDS AND REDUCED VISIBILITIES.$$
24Marine Product Recap What’s Issued for the Waters? Coastal Waters ForecastIssued four times daily (4 AM, 11 AM, 4 PM, 11 PM)5 Day forecastWinds/Waves/Precipitation (Visibility)NOWCASTNon-Routine, 2-3 hour durationIssued for sub-warning criteria weather:Mainly precipitation trendsMarine Weather StatementNon-Routine, 2+ hours durationUpdate/Continue Special Marine WarningExpire/Cancel Special Marine WarningIssued for long term sub-severe hazards lasting for longer than 2 hours that will impact marine operationsSpecial Marine WarningNon-Routine, 2 hours or lessPotentially hazardous weatherShowers/thunderstorms with winds 34 kt or greaterWaterspouts, or large hailSudden wind shift
25NWS Homepage weather.gov/washington weather.gov/baltimore Hazards highlighted on front pageUse “point and click” to view forecasts and specific hazard information
26Coastal Waters Forecast Headlines for long fused hazards listed at the top of the pageHeadlines also highlighted at the top of Coastal Waters Forecast (Small Craft Advisory, Gale Warning, etc)
30National Digital Forecast Database Graphical depiction of NWS forecast elements through 7 daysTemperatureWeatherSky CoverMany moreProgram specific sectorsPublicMarineTropicalFire WeatherZoom capability to the WFO level
31National Digital Forecast Database Zoomed into the Tidal Potomac and Chesapeake BayMarine specific elements highlightedWindsWavesWeatherHazards
32Hydrometeorological Prediction Center Current Weather Maps and AnalysesSurface Pressure ChartsForecast Maps of Surface Features
33Current Surface Map Isobars (lines of equal barometric pressure) Low PressureHigh PressureFrontsTroughsUpdated every few hours
34Current Radar Accessible through HPC site as a larger regional loop OR Local radar viewed at Baltimore/Washington siteDetects rain, snow, thunderstorms
35Current Marine Observations National Data Buoy Center (NDBC)Contains NOAA/NWS owned observation platforms
36Current Marine Observations Chesapeake Bay Interpretive Buoy System (CBIBS)NOAA owned/fundedIncludes buoys which are placed along the historic John Smith Trail
37Current Marine Observations NOAA Tides and Currents (includes PORTS)More wind obsWater level obsShort term wind/water level forecasts
38NOAA Tides and Currents PORTS – Physical Oceanographic Real Time SystemGraph gives overview of past and current…Water levelsWindsPressureTemperature
39NOAA Tides and Currents High resolution modelsForecast of winds (sustained) through 24 hoursForecast of water levels through 24 hours
40Wind-Wave Correlations WFO Baltimore-Washington forecasts significant wave heights in the local Coastal Waters Forecast (CWF) product.Significant wave heights are the average heights (trough to crest) of the one-third highest waves.For simplicity, significant wave heights are termed waves in the WFO Baltimore-Washington CWF.
41Marine Hazard Dissemination How Do We Convey the Message Today? NOAA Weather Radio (NWR)Tone Alarm (SMW) within a minute of issuanceAll marine products are broadcast on NWRWebsite (weather.gov/baltimore or weather.gov/washignton)Colorful maps on website, click to see text(http-wireless)Recorded Forecast (CWF only)(703) (menu system)Third parties (USCG) retransmit
42Marine SafetyBefore going out onto the water…BE PREPARED!! Check the latest weather forecasts. Sources include:NOAA Weather RadioTelevision Media – The Weather Channel or Local TV StationsInternet, including our website at:WEATHER.GOV/WASHINGTONWEATHER.GOV/BALTIMORE
43Marine SafetyWhile on the water…STAY ALERT!! Have a NOAA Weather Radio in your boat and continue to monitor the latest forecasts.Pay attention to changes in marine forecastsHeed any issued advisories and warnings issuedReact appropriately to observed changes of marine conditions
44Marine SafetyREMAIN ALERT for fast developing / approaching thunderstorms. Signs include:Dark, threatening clouds … increasing in number / growing verticallySteadily increasing winds / wavesFlashes of lightningHeavy static heard on AM Radio
45Marine Safety When a thunderstorm approaches: Head for shore, if possibleWhile still in the boat, make sure to have on your personal flotation device and prepare for higher winds and wavesWhen onshore, get out of the boat and seek shelter immediately
46Waterspout – west of Crisfield, MD 3:30 PM EDT Sunday September 10, 2006
47Waterspout characteristics: Short-lived ( usually <30 min.)Form from small showers or cumulus congestus)Move rapidly if associated with fast-moving shower10- to 100-feet wide; move at 5 to 75 mphVisible funnel extends from a few 100 ft up to cloud base (~2000 ft over the Ches. Bay)Spin either clockwise or counter-clockwiseVisible funnel forms from cooling of humid air due cooling/expansion (not by sucking the water!)Are called a tornado if it makes landfallAre difficult to detect by radar (little warning)Most common in late summer through the fallDO NOT GO NEAR THEM!!!!
48Waterspout life cycle: Dark spot: (light inner circle <100 ft dia. surrounded by a larger dark area of more diffuse shape/edges (no visible funnel)Spiral pattern: alternating light/dark spiral bands (vortex growth)Spray ring: swirling annulus of sea-spray (min winds ~50 mph)Mature vortex: prominent visible funnel; full spiral pattern; max winds mph; funnel extends to cloud baseDecay: can occur abruptly when inflow air is cut off; displays maximum vertical tilt
49BAD WEATHER ON THE BAY?Report your observations to the National Weather Service and help us to improve your Bay forecasts through reports of what is really happening.We are interested in winds and wave height estimates, current weather conditions, low visibilities in fog, and icing.Immediate reports have a direct impact on marine forecasts and warnings for you and your fellow mariners. However, even old reports are helpful as they can be reviewed to help improve future marine forecasts.Call our marine report hotline at or us at with your marine reports!
50Marine Reporting System Report:Location (lat/lon)Wind direction and speedWave height estimatesWeather and obstructions to visibility, if any
51Part II Outline The Atmosphere The Water Cycle Weather Instrumentation Weather BasicsCloudsFronts and air massesThunderstormsLightningHurricanes
53Layers of the Atmosphere Temperature is used to define the layers of the atmosphereThe Troposphere contains all of the weather!
54Pressure“The exertion of force upon a surface by a fluid (e.g., the atmosphere) in contact with it.”Meteorologists use areas of higher or lower pressures to forecast the weather.Low pressure systems usually come with cold fronts. High pressure systems usually build behind the cold front, allowing pleasant weather for a day or two.
56Wind Air in motion relative to the earth's surface Air moves in 3 dimensions
57Observing Wind Anemometer Wind sock Weather Vane Described with both distance and speed (mph)
58Why does the Wind Blow? Pressure Gradient Force Force is due to differences in pressure.Tries to move air to eliminate pressure differences by causing air to flow from high pressure to low pressure
59Why does the Wind Blow? 2. Coriolis Force Force is due to the earth's rotation.Causes moving objects (i.e. air, planes, birds, etc) to deflect to the right of their motion in the Northern Hemisphere
60Why does the Wind Blow? 3. Friction The earth’s surface is rough Force that causes air to slow down and spiral into lows and out of highs.
61TemperatureA measure of the internal energy that a substance contains.This is the most measured quantity in the atmosphere.
62Observing Temperature ThermometerTouchDegrees Fahrenheit (F) or Celsius (C)
63Dewpoint Temperature Measure of the moisture content in the atmosphere High Dewpoint Temperature means there is high water vapor content the air is moist or Humid
64The Water CycleThe continuous movement of water between the earth and the atmosphereFour Important Steps are…
65The Water Cycle Evaporation and Transpiration Evaporation when a substance changes from the liquid phase to the gas phaseWater Water VaporTranspiration evaporation of water through plant membranesHow water vapor, which is needed for clouds and precipitation, enters the atmosphere.
66The Water Cycle Condensation Condensation when a substance changes from the gas phase to the liquid phaseWater Vapor WaterCondensation can be observed in the atmosphere as clouds, fog, dew, or frost form.
67The Water Cycle 3. Precipitation Precipitation water, either liquid or solid, that falls from the atmosphere to the surface.Clouds are composed of millions of water droplets that have condensed. These water droplets grow into larger droplets. Eventually, the droplets can grow large enough that they will not be able to stay suspended in the cloud. When this occurs, they fall out of the cloud as precipitation.
68The Water Cycle 4. Ground Water and Runoff Groundwater precipitation is absorbed into the groundRunoff precipitation flow into streams when the ground cannot absorb any more waterSome of the runoff will evaporate and some of the groundwater will be taken in by plants and then transpired.
69PrecipitationThe process where water vapor condenses in the atmosphere to form water droplets that fall to the Earth as rain, sleet, snow, hail, etc.We want to measure what type and how much!The type depends on temperature.
70Measuring Precipitation Measure LIQUID precipitation in a rain gage.For SOLID precipitation (snow or ice), measure with a ruler. You can also melt the snow or ice and pour it in a rain gage.
71Weather InstrumentsWeather Instruments tell us what’s happening…especially for things we can’t see.We measure Wind, Precipitation, Temperature and Pressure.We use Radar, Satellites, and even Balloons!
72Doppler Radar where the radar dish is. Tower is 100 feet tall! The 30 ft. wide white ball on top iswhere the radar dish is.Radar dish inside is 25 feet wide and spins constantly. Itcan see up to 250 miles away!Radar waves sent out hit a storm cloud.Some of the radar wave bounces off the cloud back tothe radar. More waves are returned to the radar if thestorm has hail or very heavy rain. It can even tell whichway the wind is moving!
73SatellitesSatellites are sent high above the earth to take “pictures” of the clouds from above. This is a view that people usually don’t get to see.
74Weather BalloonsNWS Offices across the US release a weather balloon twice a day, once in the morning and again at night.The balloon has an Instrument packet that sends temperature, wind, and moisture data back to a computer.
75Weather BalloonsData sent back from the Instrument Pack is plotted on a graph and sent to large computer processors in Maryland to create Numerical Weather Predictions
76The basics of Weather help forecasters know… Weather-Makers!The basics of Weather help forecasters know…What will happen next?
77Forecasting the Weather In order to forecast the weather, meteorologists need to know “What’s going on?”We look at all of the parts of the weather (temperature, wind, pressure, precipitation).Then we look at what is causing the parts to behave like they do.
78Fronts and Air MassesAn air mass is a large body of air with generally uniform temperature and humidity.Fronts are the boundaries between two air masses.Fronts are classified as to which type of air mass (cold or warm) is replacing the other.
80Cloud Formation Clouds are made of water, either liquid or solid Clouds typically form when air rises.When air rises, the air's temperature cools and may reach its dewpoint temperature, at which point it becomes saturated.Once saturated, condensation occurs and the water vapor in the air will condense into tiny water droplets.As millions of droplets form, a cloud will begin to take shape.
81How to Name that Cloud!Height (High, middle, low, or vertically developing)Physical appearanceProduce precipitation
82Naming of Clouds Latin roots “cirro“ high, ‘curl of hair‘ “alto“ ‘middle‘“stratus“ layer, sheet-like, low“cumulus“ heap-like, puffy“nimbus“ clouds producing precipitationCombinations can be made of the Latin roots
83Examples Cirrus, Cirrostratus, Cirrocumulus High CloudsForm above 20,000 feet (6000 meters)Composed of ice crystalsTypically thin and white, but can be many different colors due to the angle of the sunExamples Cirrus, Cirrostratus, Cirrocumulus
84Examples Altostratus, Altocumulus Mid-level CloudsBases between 6,500 to 20,000 feet (2000 to 6000 meters)Composed of either water droplets or ice crystals depending on time of yearExamples Altostratus, Altocumulus
85Example Stratus, Stratocumulus, Nimbostratus Low CloudsBases below 6,500 feet (2000 meters)Mostly composed of water dropletsMay contain some ice particles and snow if temperatures are cold enoughExample Stratus, Stratocumulus, Nimbostratus
86Vertically Developing Clouds Span the depth of the troposphereFlat base; can grow to heights exceeding 39,000 feet (12,000 meters)They can contain both liquid droplets and ice particles.Can become powerful thunderstormsExample Cumulus, Cumulonimbus
87ThunderstormsNeeded Ingredients for a Thunderstorm: Moisture (1), Instability (2) and Lift (3)(2)(1)(3)
89LightningOne of the oldest observed natural phenomena on earth, but one of the least understood.A gigantic spark of static electricityCan be seen in volcanic eruptions, extremely intense forest fires, heavy snowstorms, large hurricanes.Most often seen in thunderstorms.Intra-cloud, Cloud-to-Ground, Cloud-to-Cloud, Cloud-to-Air
90How Much Lightning? 2,000 thunderstorms at any moment Nearly 14.5 MILLION storms each yearLightning flashes about times a second worldwide.Satellites help us see lightning around the world.
92ThunderA shock wave starts at each point along the path of the lightning bolt.Nearby lightning strikes produce thunder that is loud and short.As the shock wave moves away from the strike center, it stretches, diminishes, and becomes elongated. Then other shock waves from more distance locations arrive at the listener.At large distances from the center, the shock wave (thunder) can be many miles across. To the listener, the combination of shock waves gives thunder the continuous rumble we hear.
93TornadoesA tornado is a violently rotating column of air descending from a thunderstorm and in contact with the ground.Although tornadoes are usually brief, lasting only a few minutes, they can sometimes last for more than an hour and travel several miles causing considerable damage.
94HailHail is precipitation that is formed when updrafts in thunderstorms carry raindrops upward into extremely cold areas of the atmosphere.Hail can damage aircraft, homes and cars, and can be deadly to livestock and people.One of the people killed during the March 28, 2000 tornado in Fort Worth was killed when struck by grapefruit-size hail.La Plata, MD inches diameter on April 28, 2002Impact at speeds over 100 mph!Sign of a powerful storm .
95Flash FloodsExcept for heat related fatalities, more deaths occur from flooding than any other hazard.Most flash floods are caused by slow moving thunderstorms, thunderstorms that move repeatedly over the same area or heavy rains from tropical storms and hurricanes.These floods can develop within minutes or hours.
97Tropical Cyclone Basics Conditions that must be in place before a TC can form:a) Warm ocean waters (at least 80F) through a depth of about 150 feet.b) An atmosphere which cools fast enough with height such that it is potentially unstable to moist convection.c) Relatively moist air near the mid-levels of the atmosphere (10-18 kft).d) Generally a minimum distance of 300 miles from the equator.e) A pre-existing near surface disturbance.f) Low values (<20 kt) of vertical wind shear between the surface and the upper troposphere. Wind shear is the change of wind speed/direction with height.
98Tropical Cyclone Classification StagesSustained wind speedsTropical DepressionClosed circulation(less than 39 MPH)Tropical Storm39-73MPHHurricane74 MPH or higher
101Hurricane Hazards Katrina, 2005 in Louisiana Storm SurgeHigh WindsFloodingTornadoesKatrina, 2005 in Louisiana
102Storm SurgeGreatest potential for loss of life related to a hurricane is from a storm surge.Storm Surge= water that is pushed toward the shore by the force of the winds swirling around the storm.
103Generalizations of Storm Surge More intense storms cause higher surges.Highest surges occur usually to the right of the storm track.Fast moving storms = higher surges along the open coast.Slow moving storms=greater flooding inside bays and estuaries.
105High WindsSatellites, reconnaissance aircraft, and land based radars are used to estimate the maximum surface wind speed in a hurricane. The intensity of a land-falling hurricane is expressed in terms of categories that relate wind speeds and potential damage. NHC uses the Saffir-Simpson Hurricane scale to classify hurricanes. Each time you go up a category, the damage goes up roughly by a factor of five. So, a category four hurricane will produce 25 times more damage than a category two hurricane.
106High windsHigh rise buildings are also vulnerable to hurricane force winds, particularly at the higher levels since wind speeds tend to increase with height. Recent research suggests that winds increase one category as you go up 500 ft.This is why is not uncommon for high rise buildings to suffer a great deal of damage due to windows being blown out.
107High Winds Why do winds weaken as you go inland? They weaken due to friction caused by land and because hurricanes, once they move inland, lose their energy source which is the very warm waters of the ocean.A category four hurricane at landfall can weaken very rapidly to a category one in just six hours. This is because is a function of time and not distance, faster moving storms are going to push those winds inland more effectively than slower moving ones.
109Wind-blown debris can become deadly projectiles
110TornadoesTypically occur on the right side of the storm because of an influx of very warm moist air.As the hurricane is making landfall, winds at the surface begin to slow down due to friction, while winds a mile above the ground are still spinning very rapidly creating a favorable wind profile for tornadoes to form.
111TornadoesWhen associated with hurricanes, tornadoes are not usually accompanied by hail or a lot of lightning.Tornado production can occur for days after landfall when the TC remnants maintain an identifiable low pressure circulation.They can also develop at any time of the day or night during landfall.Classified using the Enhanced-Fujita Scale.
112Inland FloodingIntense rainfall is not directly related to the wind speed of tropical cyclones. Some of the greatest rainfall amounts occur from weaker storms that drift slowly or stall over an area.Inland flooding can be a major threat to communities hundreds of miles from the coast.In a study from 1970 to 1999, freshwater flooding accounted for more than half (59%) of U.S. tropical cyclone deaths.
113Any Questions? NWS Baltimore/Washington Marine Program Leader Contact: firstname.lastname@example.org