Marine Weather Course

1
Marine Weather Course

• NOAA National Weather Service
• Baltimore/Washington Forecast Office

2
Part I Outline

• National Weather Service Introduction
• Baltimore/Washington Forecast Office Operations
  and Marine Area
• Key Marine Products and Hazards
• Marine Observation and Forecast Information
• Marine Safety
• Marine Reporting

3
NWS Service Delivery Facilities
4
WFO Area of Responsibility
Region is prone to all weather hazards

• Maryland
• 13 Counties
• City of Baltimore
• West Virginia
• 8 Counties
• Virginia
• 22 Counties
• 11 independent cities
• District of Columbia
• River Basins
• Potomac
• Shenandoah
• Rappahannock
• Marine Area
• Tidal Potomac River
• MD Chesapeake Bay

Approximately 27,000 square miles Serving 9
Million People
5
Operations Services
Spruce Knob, Pendleton County, WV Elevation
4,861 feet

• Convective
• - Tornado Severe Thunderstorm
• Tropical Systems
• - Hurricanes Tropical Storms
• Non-Precipitable
• - Heat Waves
• - High Wind
• - Wind Chill/Excessive Cold
• Hydrological
• - Flash Floods
• - River Floods
• - Small Stream Tributaries
• Winter Storms
• Coastal Flooding
• Wildfire (Red Flag)

6
Operations Services (cont.)

• Forecasts
• - Public
• - Marine
• - Aviation
• - Fire Weather
• - River
• Support Services
• - Homeland Security
• Data Collection
• - Climate
• - Cooperative Observers

7
Marine Area
8
Key Marine Products

• Coastal Waters Forecast (CWFLWX)
• Special Marine Warnings (SMWLWX)
• Marine Weather Statements (MWSLWX)
• Nowcasts (NOWLWX)

9
Coastal Waters Forecast

• Issued a minimum of 4 times / day
• Amendments issued as necessary
• Each CWF goes out 5 days, with each period
  covering 12 hours
• Used by small pleasure boaters to large
  commercial transport ships.

10
Coastal Waters Forecast

• Elements
• Synopsis Short, concise
• Headlines of long duration hazards Advisories,
  Watches, Warnings
• Wind from 8 compass points, in knots (kt)
• Waves wave heights, in feet (ft)
• Weather thunderstorms, rain, snow and fog
  (significant visibility reduction)

11
Long Duration Hazards

• Small Craft Advisory (Tidal Potomac and
  Chesapeake Bay) -- the following conditions are
  occurring or expected to begin within the first 3
  forecast periods
• Sustained winds 18-33 kt
• Frequent gusts 18-33 kt
• (frequent refers to lasting gt 2 hours)
• Waves 4 ft

12
Long Duration Hazards

• Gale Warning (Tidal Potomac and Chesapeake Bay)
  -- the following conditions are occurring or
  expected to begin within the first 3 forecast
  periods
• Sustained winds 34-47 kt
• Frequent gusts 34-47 kt

13
Long Duration Hazards

• Storm Warning (Tidal Potomac and Chesapeake Bay)
  -- the following conditions are occurring or
  expected to begin within the first 3 forecast
  periods
• Sustained winds 48-63 kt
• Frequent gusts 48-63 kt

14
Long Duration Hazards

• Hurricane 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 greater
• Frequent gusts 64 kt or greater
• Not associated with a tropical system

15
Tropical Hazards

• Tropical Watches/Warnings
• Initiated by National Hurricane Center in Miami
• nhc.noaa.gov
• Tropical Storm (sustained winds 34 to 63 kt / 39
  to 73 mph)
• Hurricane (sustained winds gt 64 kt / gt 74 mph)

Isabel, 2003
16
Convective Hazards

• Severe Local Storm Watches
• Initiated by Storm Prediction Center in Norman,
  OK
• spc.noaa.gov
• Tornado Watch
• Severe Thunderstorm Watch

17
Coastal Waters Forecast

• ANZ535-536-231930-
• /X.EXT.KLWX.SC.Y.0037.051023T1200Z-051023T2200Z/
• TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD-
• TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND-
• 337 AM EDT SUN OCT 23 2005
• ...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 OF
• SHOWERS.
• .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.

18
Special 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
  greater
• Waterspouts

19
Special Marine Warnings

• BULLETIN - IMMEDIATE BROADCAST REQUESTED
• SPECIAL MARINE WARNING
• NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON
  DC
• 621 PM EST SUN NOV 6 2005
• THE 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...

20
Marine Weather Statements

• Update/Continue Special Marine Warning
• Expire/Cancel Special Marine Warning
• Issued for long term sub-severe hazards lasting
  for longer than 2 hours that will impact marine
  operations

21
Marine Weather Statements

• MARINE WEATHER STATEMENT
• NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON
  DC
• 1045 AM EDT SUN AUG 7 2005
• ANZ531-071545-
• /O.CON.KLWX.MA.W.0106.000000T0000Z-050807T1545Z/
• 1045 AM EDT SUN AUG 7 2005
• ...A SPECIAL MARINE WARNING CONTINUES UNTIL 1145
  AM EDT...
• FOR THE FOLLOWING AREA...
• CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT,
  MD
• AT 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.

22
Nowcasts

• Issued 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.

23
Nowcasts

• SHORT TERM FORECAST
• NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON
  DC
• 804 AM EDT FRI OCT 21 2005
• ANZ530gt537-DCZ001-MDZ005gt007-009gt011-013-014-016gt0
  18-VAZ041-042- 052gt057-211330-
• ANNE ARUNDEL MD-ARLINGTON/FALLS CHURCH/ALEXANDRIA
  VA-CALVERT MD-CARROLL MD-CHARLES MD-DISTRICT OF
• COLUMBIA 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-SOUTHERN
• BALTIMORE 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-
  
• 804 AM EDT FRI OCT 21 2005

24
Marine Product RecapWhats Issued for the Waters?
Coastal Waters Forecast Issued four times daily(4 AM, 11 AM, 4 PM, 11 PM) 5 Day forecast Winds/Waves/Precipitation (Visibility)
NOWCAST Non-Routine, 2-3 hour duration Issued for sub-warning criteria weather Mainly precipitation trends
Marine Weather Statement Non-Routine, 2 hours duration Update/Continue Special Marine Warning Expire/Cancel Special Marine Warning Issued for long term sub-severe hazards lasting for longer than 2 hours that will impact marine operations
Special Marine Warning Non-Routine, 2 hours or less Potentially hazardous weather Showers/thunderstorms with winds 34 kt or greater Waterspouts, or large hail Sudden wind shift
25
NWS Homepage

• weather.gov/washington
• weather.gov/baltimore
• Hazards highlighted on front page
• Use point and click to view forecasts and
  specific hazard information

26
Coastal Waters Forecast

• Coastal Waters Forecast
• Headlines for long fused hazards listed at the
  top of the page
• Headlines also highlighted at the top of Coastal
  Waters Forecast (Small Craft Advisory, Gale
  Warning, etc)

27
Hazardous Weather Outlook
28
Hazardous Weather Outlook

• Alerts public to potential hazards and their
  impact
• Potential hazards over the next 7 days
• Marine hazards
• Coastal hazards

29
Marine Weather Message
30
National Digital Forecast Database

• Graphical depiction of NWS forecast elements
  through 7 days
• Temperature
• Weather
• Sky Cover
• Many more
• Program specific sectors
• Public
• Marine
• Tropical
• Fire Weather
• Zoom capability to the WFO level

31
National Digital Forecast Database

• Zoomed into the Tidal Potomac and Chesapeake Bay
• Marine specific elements highlighted
• Winds
• Waves
• Weather
• Hazards

www.weather.gov/forecasts/graphical
32
Hydrometeorological Prediction Center

• http//www.hpc.ncep.noaa.gov/
• Current Weather Maps and Analyses
• Surface Pressure Charts
• Forecast Maps of Surface Features

33
Current Surface Map

• Isobars (lines of equal barometric pressure)
• Low Pressure
• High Pressure
• Fronts
• Troughs
• Updated every few hours

34
Current Radar

• Accessible through HPC site as a larger regional
  loop OR
• Local radar viewed at Baltimore/Washington site
• Detects rain, snow, thunderstorms

35
Current Marine Observations

• National Data Buoy Center (NDBC)
• http//www.ndbc.noaa.gov/
• Contains NOAA/NWS owned observation platforms

36
Current Marine Observations

• Chesapeake Bay Interpretive Buoy System (CBIBS)
• NOAA owned/funded
• Includes buoys which are placed along the
  historic John Smith Trail

37
Current Marine Observations

• NOAA Tides and Currents (includes PORTS)
• http//tidesandcurrents.noaa.gov/
• More wind obs
• Water level obs
• Short term wind/water level forecasts

38
NOAA Tides and Currents

• PORTS Physical Oceanographic Real Time System
• Graph gives overview of past and current
• Water levels
• Winds
• Pressure
• Temperature

39
NOAA Tides and Currents

• High resolution models
• Forecast of winds (sustained) through 24 hours
• Forecast of water levels through 24 hours

40
Wind-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.
  

41
Marine Hazard DisseminationHow Do We Convey the
Message Today?

• NOAA Weather Radio (NWR)
• Tone Alarm (SMW) within a minute of issuance
• All marine products are broadcast on NWR

• Website (weather.gov/baltimore or
  weather.gov/washignton)
• Colorful maps on website, click to see text
• http/mobile.srh.noaa.gov (http-wireless)

• Recorded Forecast (CWF only)
• [phone] (menu system)

• Third parties (USCG) retransmit

42
Marine Safety

• Before going out onto the waterBE PREPARED!!
  Check the latest weather forecasts. Sources
  include
• NOAA Weather Radio
• Television Media The Weather Channel or Local
  TV Stations
• Internet, including our website at
• WEATHER.GOV/WASHINGTON
• WEATHER.GOV/BALTIMORE

43
Marine Safety

• While on the waterSTAY ALERT!! Have a NOAA
  Weather Radio in your boat and continue to
  monitor the latest forecasts.
• Pay attention to changes in marine forecasts
• Heed any issued advisories and warnings issued
• React appropriately to observed changes of marine
  conditions

44
Marine Safety

• REMAIN ALERT for fast developing / approaching
  thunderstorms. Signs include
• Dark, threatening clouds increasing in number /
  growing vertically
• Steadily increasing winds / waves
• Flashes of lightning
• Heavy static heard on AM Radio

45
Marine Safety

• When a thunderstorm approaches
• Head for shore, if possible
• While still in the boat, make sure to have on
  your personal flotation device and prepare for
  higher winds and waves
• When onshore, get out of the boat and seek
  shelter immediately

46
Waterspout west of Crisfield, MD 330 PM EDT
Sunday September 10, 2006
47

• Waterspout characteristics
• Short-lived ( usually lt30 min.)
• Form from small showers or cumulus congestus)
• Move rapidly if associated with fast-moving
  shower
• 10- to 100-feet wide move at 5 to 75 mph
• Visible funnel extends from a few 100 ft up to
  cloud base (2000 ft over the Ches. Bay)
• Spin either clockwise or counter-clockwise
• Visible funnel forms from cooling of humid air
  due cooling/expansion (not by sucking the water!)
• Are called a tornado if it makes landfall
• Are difficult to detect by radar (little warning)
• Most common in late summer through the fall
• DO NOT GO NEAR THEM!!!!

48

• Waterspout life cycle
• Dark spot (light inner circle lt100 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 60-100 mph funnel
  extends to cloud base
• Decay can occur abruptly when inflow air is cut
  off displays maximum vertical tilt

49
BAD 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 1-800-253-7091
  or email us at lwx-report_at_noaa.gov with your
  marine reports!

50
Marine Reporting System

• 1-800-253-7091
• Report
• Location (lat/lon)
• Wind direction and speed
• Wave height estimates
• Weather and obstructions to visibility, if any

51
Part II Outline

• The Atmosphere
• The Water Cycle
• Weather Instrumentation
• Weather Basics
• Clouds
• Fronts and air masses
• Thunderstorms
• Lightning
• Hurricanes

52
Earths Atmosphere
53
Layers of the Atmosphere

• Temperature is used to define the layers of the
  atmosphere
• The Troposphere contains all of the weather!

54
Pressure

• 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.

55
Measuring Pressure

• Barometer

56
Wind

• Air in motion relative to the earth's surface
• Air moves in 3 dimensions

57
Observing Wind

• Anemometer
• Wind sock
• Weather Vane
• Described with both distance and speed (mph)

58
Why 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

59
Why 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

60
Why does the Wind Blow?

• 3. Friction
• The earths surface is rough
• Force that causes air to slow down and spiral
  into lows and out of highs.

61
Temperature

• A measure of the internal energy that a substance
  contains.
• This is the most measured quantity in the
  atmosphere.

62
Observing Temperature

• Thermometer
• Touch
• Degrees Fahrenheit (F) or Celsius (C)

63
Dewpoint 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

64
The Water Cycle

• The continuous movement of water between the
  earth and the atmosphere
• Four Important Steps are

65
The Water Cycle

• Evaporation and Transpiration
• Evaporation ? when a substance changes from the
  liquid phase to the gas phase
• Water ? Water Vapor
• Transpiration ? evaporation of water through
  plant membranes
• How water vapor, which is needed for clouds and
  precipitation, enters the atmosphere.

66
The Water Cycle

• Condensation
• Condensation ? when a substance changes from the
  gas phase to the liquid phase
• Water Vapor ? Water
• Condensation can be observed in the atmosphere as
  clouds, fog, dew, or frost form.

67
The 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.

68
The Water Cycle

• 4. Ground Water and Runoff
• Groundwater ? precipitation is absorbed into the
  ground
• Runoff ? precipitation flow into streams
  when the ground cannot absorb any more water
• Some of the runoff will evaporate and some of the
  groundwater will be taken in by plants and then
  transpired.

69
Precipitation

• The 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.

70
Measuring 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.

71
Weather Instruments

• Weather Instruments tell us whats
  happeningespecially for things we cant see.
• We measure Wind, Precipitation, Temperature and
  Pressure.
• We use Radar, Satellites, and even Balloons!

72
Doppler Radar

• Tower is 100 feet tall! The 30 ft. wide white
  ball on top is
• where the radar dish is.
• Radar dish inside is 25 feet wide and spins
  constantly. It
• can see up to 250 miles away!
• Radar waves sent out hit a storm cloud.
• Some of the radar wave bounces off the cloud
  back to
• the radar. More waves are returned to the
  radar if the
• storm has hail or very heavy rain. It can even
  tell which
• way the wind is moving!

73
Satellites

• Satellites are sent high above the earth to take
  pictures of the clouds from above. This is a
  view that people usually dont get to see.

74
Weather Balloons

• NWS 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.

75
Weather Balloons

• Data sent back from the Instrument Pack is
  plotted on a graph and sent to large computer
  processors in Maryland to create Numerical
  Weather Predictions

76
Weather-Makers!

• The basics of Weather help forecasters know
• What will happen next?

77
Forecasting the Weather

• In order to forecast the weather, meteorologists
  need to know Whats 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.

78
Fronts and Air Masses

• An 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.

79
Clouds
80
Cloud 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.

81
How to Name that Cloud!

• Height (High, middle, low, or vertically
  developing)
• Physical appearance
• Produce precipitation

82
Naming of Clouds

• Latin roots
• cirro ? high, curl of hair
• alto ? middle
• stratus ? layer, sheet-like, low
• cumulus ? heap-like, puffy
• nimbus ? clouds producing precipitation
• Combinations can be made of the Latin roots

83
High Clouds

• Form above 20,000 feet (6000 meters)
• Composed of ice crystals
• Typically thin and white, but can be many
  different colors due to the angle of the sun

Examples ? Cirrus, Cirrostratus, Cirrocumulus
84
Mid-level Clouds

• Bases between 6,500 to 20,000 feet (2000 to 6000
  meters)
• Composed of either water droplets or ice crystals
  depending on time of year

Examples ? Altostratus, Altocumulus
85
Low Clouds

• Bases below 6,500 feet (2000 meters)
• Mostly composed of water droplets
• May contain some ice particles and snow if
  temperatures are cold enough

Example ? Stratus, Stratocumulus, Nimbostratus
86
Vertically Developing Clouds

• Span the depth of the troposphere
• Flat base can grow to heights exceeding 39,000
  feet (12,000 meters)
• They can contain both liquid droplets and ice
  particles.
• Can become powerful thunderstorms

Example ? Cumulus, Cumulonimbus
87
Thunderstorms

• Needed Ingredients for a Thunderstorm Moisture
  (1), Instability (2) and Lift (3)

(2)
(1)
(3)
88
Thunderstorm Hazards

• Lightning
• Flash Floods
• Hail
• Tornadoes

89
Lightning

• One of the oldest observed natural phenomena on
  earth, but one of the least understood.
• A gigantic spark of static electricity
• Can 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

90
How Much Lightning?

• 2,000 thunderstorms at any moment
• Nearly 14.5 MILLION storms each year
• Lightning flashes about 40 times a second
  worldwide.
• Satellites help us see lightning around the world.

91
How Lightning is Created
92
Thunder

• A 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. 

93
Tornadoes

• A 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.

94
Hail

• Hail 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 - 4.5 inches diameter on April 28,
  2002
• Impact at speeds over 100 mph!
• Sign of a powerful storm .

95
Flash Floods

• Except 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.

96
Tropical Cyclones
97
Tropical 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 (lt20 kt) of vertical wind shear
  between the surface and the upper troposphere.
  Wind shear is the change of wind speed/direction
  with height.

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Tropical Cyclone Classification
Stages Sustained wind speeds
Tropical Depression Closed circulation (less than 39 MPH)
Tropical Storm 39-73MPH
Hurricane 74 MPH or higher
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Saffir-Simpson Hurricane Scale(based on wind
speed alone)
Category Wind Speed (MPH) Damage
1 74-95 Minimal
2 96-110 Moderate
3 111-130 Extensive
4 131-155 Extreme
5 gt155 Catastrophic
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TC Structure
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Hurricane Hazards

• Storm Surge
• High Winds
• Flooding
• Tornadoes

Katrina, 2005 in Louisiana
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Storm Surge

• Greatest 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.

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Generalizations 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 stormsgreater flooding inside bays
  and estuaries.

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Storm Surge
105
High Winds

• Satellites, 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.

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High winds

• High 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.

107
High 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.

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Damage done by Andrew 1992
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Wind-blown debris can become deadly projectiles
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Tornadoes

• Typically 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.

111
Tornadoes

• When 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.

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Inland Flooding

• Intense 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.

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Any Questions?NWS Baltimore/WashingtonMarine
Program Leader Contact brandon.peloquin_at_noaa.gov