BULLETIN
Tropical Storm Laura Advisory Number 20
NWS National Hurricane Center Miami FL AL132020
500 PM EDT Mon Aug 24 2020
...CENTER OF LAURA PASSING NEAR THE ISLE OF YOUTH....
...HURRICANE AND STORM SURGE WATCHES ISSUED FOR A PORTION OF THE
NORTHWEST GULF COAST...
SUMMARY OF 500 PM EDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...21.7N 82.2W
ABOUT 40 MI...65 KM E OF THE ISLE OF YOUTH
ABOUT 175 MI...280 KM E OF THE WESTERN TIP OF CUBA
MAXIMUM SUSTAINED WINDS...60 MPH...95 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 20 MPH...31 KM/H
MINIMUM CENTRAL PRESSURE...1001 MB...29.56 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:
A Storm Surge Watch is in effect from San Luis Pass, Texas, to Ocean
Springs, Mississippi, including Lake Pontchartrain, Lake Maurepas,
and Lake Borgne for areas outside of the southeast Louisiana
Hurricane and Storm Damage Risk Reduction System.
A Hurricane Watch is in effect from Port Bolivar, Texas, to
west of Morgan City, Louisiana.
A Tropical Storm Watch is in effect from south of Port Bolivar to
San Luis Pass Texas and from Morgan City to the Mouth of the
Mississippi River.
The Tropical Storm Warning for Little Cayman and Cayman Brac has
been discontinued.
The Tropical Storm Warning for the Cuban provinces of Camaguey and
Las Tunas has been discontinued.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT:
A Storm Surge Watch is in effect for...
* San Luis Pass Texas to Ocean Springs Mississippi
* Lake Pontchartrain, Lake Maurepas, and Lake Borgne
A Hurricane Watch is in effect for...
* Port Bolivar Texas to west of Morgan City Louisiana
A Tropical Storm Warning is in effect for...
* Cuban provinces of Ciego De Avila, Sancti Spiritus, Villa Clara,
Cienfuegos, Matanzas, Mayabeque, La Habana, Artemisa, Pinar del
Rio, and the Isle of Youth
* Florida Keys from Craig Key to Key West
* Dry Tortugas
A Tropical Storm Watch is in effect for...
* South of Port Bolivar to San Luis Pass Texas
* Morgan City Louisiana to the Mouth of the Mississippi River
A Storm Surge Watch means there is a possibility of life-
threatening inundation, from rising water moving inland from the
coastline, in the indicated locations during the next 48 hours.
For a depiction of areas at risk, please see the National Weather
Service Storm Surge Watch/Warning Graphic, available at
hurricanes.gov.
A Hurricane Watch means that hurricane conditions are possible
within the watch area. A watch is typically issued 48 hours
before the anticipated first occurrence of tropical-storm-force
winds, conditions that make outside preparations difficult or
dangerous.
A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area.
A Tropical Storm Watch means that tropical storm conditions are
possible within the watch area, generally within 48 hours.
For storm information specific to your area in the United
States, including possible inland watches and warnings, please
monitor products issued by your local National Weather Service
forecast office. For storm information specific to your area
outside of the United States, please monitor products issued by
your national meteorological service.
DISCUSSION AND OUTLOOK
----------------------
At 500 PM EDT (2100 UTC), the center of Tropical Storm Laura was
located near latitude 21.7 North, longitude 82.2 West. Laura is
moving toward the west-northwest near 20 mph (31 km/h), and this
general motion with some decrease in forward speed is expected over
the next day or so. A turn toward the northwest is forecast by
Wednesday, and a northwestward to north-northwestward motion should
continue through Wednesday night. On the forecast track, the center
of Laura will cross western Cuba this evening and move into the
southeastern Gulf of Mexico overnight. Laura is then forecast to
move over the central and northwestern Gulf of Mexico Tuesday night
and Wednesday, and approach the northwestern coast of the Gulf of
Mexico Wednesday night.
Maximum sustained winds are near 60 mph (95 km/h) with higher gusts.
Strengthening is expected when the storm moves over the Gulf of
Mexico, and Laura is foreast to become a hurricane by late Tuesday.
Additional strengthening is forecast on Wednesday.
Tropical-storm-force winds extend outward up to 175 miles (280 km)
primarily to the northeast and east of the center.
The estimated minimum central pressure is 1001 mb (29.56 inches).
HAZARDS AFFECTING LAND
----------------------
Key messages for Laura can be found in the Tropical Cyclone
Discussion under AWIPS header MIATCDAT3 and WMO header WTNT43 KNHC.
STORM SURGE: The combination of a dangerous storm surge and the
tide will cause normally dry areas near the coast to be flooded by
rising waters moving inland from the shoreline. The water could
reach the following heights above ground somewhere in the indicated
areas if the peak surge occurs at the time of high tide...
High Island TX to Morgan City LA including Sabine Lake, Calcasieu
Lake, and Vermilion Bay...7-11 ft
Port Bolivar TX to High Island TX...4-6 ft
Morgan City LA to Mouth of the Mississippi River...4-6 ft
Mouth of the Mississippi River to Ocean Springs MS including Lake
Borgne...3-5 ft
San Luis Pass TX to Port Bolivar TX...2-4 ft
Galveston Bay...2-4 ft
Lake Pontchartrain and Lake Maurepas...2-4 ft
The deepest water will occur along the immediate coast near and to
the right of the landfall location, where the surge will be
accompanied by large and destructive waves. Surge-related
flooding depends on the relative timing of the surge and the tidal
cycle, and can vary greatly over short distances. For information
specific to your area, please see products issued by your local
National Weather Service forecast office.
RAINFALL: Laura is expected to produce the following storm total
rainfall accumulations into tonight:
Western Jamaica, Western Cuba and the Cayman Islands: 4 to 6 inches,
with maximum amounts of 10 inches. Across the Greater Antilles this
heavy rainfall could lead to life-threatening flash and urban
flooding, and the potential for mudslides.
From Wednesday afternoon into Saturday, Laura is expected to produce
rainfall of 4 to 8 inches, with isolated maximum amounts of 12
inches across portions of the west-central U.S. Gulf Coast near the
Texas and Louisiana border north into portions of the lower
Mississippi Valley. This rainfall could cause widespread flash and
urban flooding, small streams to overflow their banks, and minor to
isolated moderate river flooding.
WIND: Tropical storm conditions are expected to spread westward
within the warning area in western Cuba through this evening.
Tropical storm conditions are also expected within the warning area
in the middle and lower Florida Keys and the Dry Tortugas tonight.
Hurricane conditions are possible in the hurricane watch area along
the Gulf Coast by late Wednesday, with tropical storm conditions
possible by Wednesday afternoon.
SURF: Swells generated by Laura are affecting portions of Cuba, the
central Bahamas, and the Florida Keys. Swells are expected to
spread northward along portions of the west coast of Florida
peninsula and the coast of the Florida panhandle on Tuesday
and Tuesday night, and reach the northern and northwest Gulf coast
by Wednesday. These swells are likely to cause life-threatening surf
and rip current conditions. Please consult products from your
local weather office.
TORNADOES: An isolated tornado is possible through tonight across
the Florida Keys.
NEXT ADVISORY
-------------
Next intermediate advisory at 800 PM EDT.
Next complete advisory at 1100 PM EDT.
$$
Forecaster Brown
Tropical Storm Laura Discussion Number 20
NWS National Hurricane Center Miami FL AL132020
500 PM EDT Mon Aug 24 2020
The satellite presentation of the tropical storm has improved
somewhat with deep convection remaining over the center, and an
increase in banding over the southeastern portion of the
circulation. Earlier aircraft and scatterometer data, however,
indicated that there has been little change in strength today, and
the initial intensity remains 50 kt. These observations have shown
the the stronger winds are located in the convective band well east
and southeast of the center, and that the system currently lacks
an inner core. This is likely the reason that Laura has not been
able to strengthen while it has moved over water today. The
aircraft also reported a fairly stable minimum pressure of 1001-1003
mb during its mission this morning and early afternoon.
The intensity forecast philosophy remains the same as the previous
advisory. Once Laura moves over the southeastern Gulf of Mexico
tonight, a combination of warm sea surface temperatures and low
vertical wind shear should allow for steady strengthening. The
latest iterations of the global and regional hurricane models
continue to show significant deepening while Laura traverses the
Gulf of Mexico, and a period or rapid strengthening is possible once
an inner core is able to organize. The statistical guidance is
again on the lower side of the intensity forecast envelope
while the HWRF and CTCI models bringing Laura to major hurricane
strength. The NHC intensity forecast is again between these
solutions and is close to the consensus aids.
The initial motion estimate is 290/16 kt. A deep-layer ridge over
the western Atlantic is expected to build westward during the next
day or so. By early Wednesday, a mid- to upper-level trough over
the south-central United States is forecast to erode the western
portion of the ridge, which should cause Laura to turn northwestward
and then northward toward the northwestern Gulf coast. After
landfall, Laura or its remnants are expected to become embedded
in the mid-latitude westerlies and recurve over the eastern U.S.
on days 4 and 5. The latest runs of the dynamical models are in a
little better agreement, but the 1200 UTC ECMWF ensemble mean is
located considerably left of its deterministic run, indicating that
uncertainty regarding the track forecast remains. Users are again
reminded to not to focus on the exact details of the track or
intensity forecasts as the average NHC track error at 60 h is
around 90 miles and the average intensity error is close to 15 mph.
In addition, wind, storm surge, and rainfall hazards will extend
far from the center.
The new NHC forecast necessitates the issuance of storm surge and
hurricane watches for portions of the U.S. Gulf Coast.
Key Messages:
1. Laura is forecast to reach the northwestern Gulf Coast as a
hurricane late Wednesday and early Thursday. Do not focus
on the details of the official forecast given the typical
uncertainty in NHC's 2 to 3 day track and intensity predictions. In
addition, storm surge, wind, and rainfall hazards will extend well
away from Laura's center along the Gulf Coast.
2. There is a risk of life-threatening storm surge from San Luis
Pass, Texas, to Ocean Springs, Mississippi, within the next 48
hours, and a storm surge watch has been issued for these areas
outside of the southeast Louisiana Hurricane and Storm Damage Risk
Reduction System. Residents in these areas should follow any advice
given by local officials.
3. Hurricane conditions are possible by late Wednesday from Port
Bolivar, Texas, to west of Morgan City, Louisiana, with tropical
storm conditions possible by Wednesday afternoon, and a hurricane
watch has been issued. Additional hurricane watches may be needed
farther south along the Texas coast if the track forecast shifts
toward the south and west tonight and Tuesday.
4. Tropical storm conditions and heavy rainfall are expected across
central and western Cuba through tonight. These rains could cause
mudslides and life-threatening flash and urban flooding.
FORECAST POSITIONS AND MAX WINDS
INIT 24/2100Z 21.7N 82.2W 50 KT 60 MPH
12H 25/0600Z 22.7N 84.5W 50 KT 60 MPH
24H 25/1800Z 24.2N 87.4W 60 KT 70 MPH
36H 26/0600Z 25.7N 90.0W 75 KT 85 MPH
48H 26/1800Z 27.5N 92.0W 85 KT 100 MPH
60H 27/0600Z 29.8N 93.1W 90 KT 105 MPH
72H 27/1800Z 32.5N 93.0W 45 KT 50 MPH...INLAND
96H 28/1800Z 36.1N 90.0W 25 KT 30 MPH...INLAND
120H 29/1800Z 36.5N 80.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
$$
Forecaster Brown