Title: Marine Weather Course
1Marine Weather Course
- NOAA National Weather Service
- Baltimore/Washington Forecast Office
2Part 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
3NWS Service Delivery Facilities
4WFO 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
5Operations 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)
6Operations Services (cont.)
- Forecasts
- - Public
- - Marine
- - Aviation
- - Fire Weather
- - River
- Support Services
- - Homeland Security
- Data Collection
- - Climate
- - Cooperative Observers
7Marine Area
8Key Marine Products
- Coastal Waters Forecast (CWFLWX)
- Special Marine Warnings (SMWLWX)
- Marine Weather Statements (MWSLWX)
- Nowcasts (NOWLWX)
9Coastal 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.
10Coastal 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)
11Long 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
12Long 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
13Long 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
14Long 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
15Tropical 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
16Convective Hazards
- Severe Local Storm Watches
- Initiated by Storm Prediction Center in Norman,
OK - spc.noaa.gov
- Tornado Watch
- Severe Thunderstorm Watch
17Coastal 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.
-
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
greater - Waterspouts
19Special 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...
20Marine 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
21Marine 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.
22Nowcasts
- 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.
23Nowcasts
- 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
24Marine 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
25NWS Homepage
- weather.gov/washington
- weather.gov/baltimore
- Hazards highlighted on front page
- Use point and click to view forecasts and
specific hazard information
26Coastal 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)
27Hazardous Weather Outlook
28Hazardous Weather Outlook
- Alerts public to potential hazards and their
impact - Potential hazards over the next 7 days
- Marine hazards
- Coastal hazards
29Marine Weather Message
30National 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
31National Digital Forecast Database
- Zoomed into the Tidal Potomac and Chesapeake Bay
- Marine specific elements highlighted
- Winds
- Waves
- Weather
- Hazards
www.weather.gov/forecasts/graphical
32Hydrometeorological Prediction Center
- http//www.hpc.ncep.noaa.gov/
- Current Weather Maps and Analyses
- Surface Pressure Charts
- Forecast Maps of Surface Features
33Current Surface Map
- Isobars (lines of equal barometric pressure)
- Low Pressure
- High Pressure
- Fronts
- Troughs
- Updated every few hours
34Current Radar
- Accessible through HPC site as a larger regional
loop OR - Local radar viewed at Baltimore/Washington site
- Detects rain, snow, thunderstorms
35Current Marine Observations
- National Data Buoy Center (NDBC)
- http//www.ndbc.noaa.gov/
- Contains NOAA/NWS owned observation platforms
36Current Marine Observations
- Chesapeake Bay Interpretive Buoy System (CBIBS)
- NOAA owned/funded
- Includes buoys which are placed along the
historic John Smith Trail
37Current Marine Observations
- NOAA Tides and Currents (includes PORTS)
- http//tidesandcurrents.noaa.gov/
- More wind obs
- Water level obs
- Short term wind/water level forecasts
38NOAA Tides and Currents
- PORTS Physical Oceanographic Real Time System
- Graph gives overview of past and current
- Water levels
- Winds
- Pressure
- Temperature
39NOAA Tides and Currents
- High resolution models
- Forecast of winds (sustained) through 24 hours
- Forecast 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 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)
- (703) 996-2200 (menu system)
- Third parties (USCG) retransmit
42Marine 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
43Marine 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
44Marine 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
45Marine 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
46Waterspout 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
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 1-800-253-7091
or email us at lwx-report_at_noaa.gov with your
marine reports!
50Marine Reporting System
- 1-800-253-7091
- Report
- Location (lat/lon)
- Wind direction and speed
- Wave height estimates
- Weather and obstructions to visibility, if any
51Part II Outline
- The Atmosphere
- The Water Cycle
- Weather Instrumentation
- Weather Basics
- Clouds
- Fronts and air masses
- Thunderstorms
- Lightning
- Hurricanes
52Earths Atmosphere
53Layers of the Atmosphere
- Temperature is used to define the layers of the
atmosphere - The 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.
55Measuring Pressure
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 earths surface is rough
- Force that causes air to slow down and spiral
into lows and out of highs.
61Temperature
- A measure of the internal energy that a substance
contains. - This is the most measured quantity in the
atmosphere.
62Observing Temperature
- Thermometer
- Touch
- Degrees 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 Cycle
- The continuous movement of water between the
earth and the atmosphere - Four Important Steps are
65The 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.
66The 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.
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
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.
69Precipitation
- 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.
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 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!
72Doppler 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!
73Satellites
- 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.
74Weather 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.
75Weather 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
76Weather-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 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.
78Fronts 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.
79Clouds
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 appearance
- Produce 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 precipitation
- Combinations can be made of the Latin roots
83High 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
84Mid-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
85Low 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
86Vertically 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
87Thunderstorms
- Needed Ingredients for a Thunderstorm Moisture
(1), Instability (2) and Lift (3)
(2)
(1)
(3)
88Thunderstorm Hazards
- Lightning
- Flash Floods
- Hail
- Tornadoes
89Lightning
- 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
90How 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.
91How Lightning is Created
92Thunder
- 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.
93Tornadoes
- 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.
94Hail
- 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 .
95Flash 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.
96Tropical Cyclones
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 (lt20 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
Stages Sustained wind speeds
Tropical Depression Closed circulation (less than 39 MPH)
Tropical Storm 39-73MPH
Hurricane 74 MPH or higher
99Saffir-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
100TC Structure
101Hurricane Hazards
- Storm Surge
- High Winds
- Flooding
- Tornadoes
Katrina, 2005 in Louisiana
102Storm 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.
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 stormsgreater flooding inside bays
and estuaries.
104Storm Surge
105High 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.
106High 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.
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.
108Damage done by Andrew 1992
109Wind-blown debris can become deadly projectiles
110Tornadoes
- 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.
111Tornadoes
- 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.
112Inland 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.
113Any Questions?NWS Baltimore/WashingtonMarine
Program Leader Contact brandon.peloquin_at_noaa.gov