Track:
https://www.nhc.noaa.gov/refresh/graphics_at3+shtml/?cone#contents
Tropical Storm Laura Discussion Number 18
NWS National Hurricane Center Miami FL AL132020
500 AM EDT Mon Aug 24 2020
Satellite data indicate that Laura has moved back over the warm
waters of the Caribbean Sea south of Cuba. Modest northerly vertical
wind shear has kept the bulk of the deep convection displaced into
the southern semicircle of Laura's circulation. Earlier ASCAT-B/-C
scatterometer passes around 0210Z-0250Z revealed a small
circulation just offshore southeastern Cuba. However, this feature
is considered to be a leeside vortex, possibly having developed in
response to the long-fetch southerly low-level flow passing over
Jamaica, and not the primary low-level center associated with Laura.
The initial intensity is being maintained at 55 kt based on 43-46 kt
wind vectors located just offshore southeastern Cuba that were
present in the aforementioned ASCAT data, and allowing for some
undersampling by the scatterometer instrument.
The initial motion estimate is 290/18 kt. The deep-layer
Bermuda-Azores ridge to the north of the cyclone is forecast by all
of the models to build and expand westward across the Bahamas,
Florida, and into the eastern and central Gulf of Mexico over the
new few days. This dominant steering flow pattern is expected to
keep Laura moving west-northwestward just offshore the southern
coast of Cuba today, followed by the cyclone emerging over the
southeastern Gulf of Mexico on Tuesday. By late Tuesday and early
Wednesday, a mid- to upper-level trough located over the
south-central U.S. is forecast to pinch off and dig southwestward
and merge with the remnants of Tropical Storm Marco over the western
Gulf of Mexico, eroding the western extent of the ridge in the
process. This is expected to cause Laura to slow down and gradually
turn northwestward and then northward toward the northwestern Gulf
coast by late Wednesday and early Thursday. The latest NHC model
guidance is in excellent agreement on this developing synoptic
pattern, and the official forecast is similar to but slightly left
or south of the previous advisory track to account for the expected
northerly to northeasterly wind shear keeping the convection and
low-level center displaced to the south for the next 24 hours or so.
On the forecast track, Laura is expected to remain just offshore the
southern Cuba today, move into the Gulf of Mexico by early Tuesday
morning, and approach the U..S northwest Gulf coast area Wednesday
night and early Thursday.
Since Laura's center is expected to remain over water just south of
Cuba, there is the possibility that some slight strengthening could
occur today or tonight before the cyclone reaches the Gulf of Mexico
in 24 hours. After that, Laura will be moving over the very warm
and deep waters of Gulf Stream and Loop Current located over the
southeastern Gulf, which could trigger a brief period of rapid
intensification. The GFS and ECMWF models, along with the
statistical and corrected-consensus models, only strengthen the
cyclone to a peak intensity around 75 kt. In contrast, the HRWF and
HMON models bring Laura to major hurricane strength by 60 hours.
Given the very favorable environmental conditions of high SSTs near
31 deg C and low vertical shear values less than 10 kt after 24-36
hours, subsequent intensity forecasts might have to trend more
toward the regional models. But for now, the official intensity
forecast will continue to follow a blend of the regional and global
model intensity forecasts, and lies at the high-end of the
intensity guidance at 60 and 72 hours.
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
72 h is around 100 miles and the average intensity error is around
15 mph (13 kt). In addition, winds, storm surge, and rainfall
hazards will extend far from the center.
Key Messages:
1. Tropical storm conditions are expected across much of Cuba
today. Heavy rainfall is likely across Cuba and Jamaica today, and
these rains could cause mudslides and life-threatening flash and
urban flooding. Tropical storm conditions are expected in the Dry
Tortugas, and the Middle and Lower Florida Keys later today.
2. While the details of the long-range track and intensity forecasts
remain uncertain, Laura is forecast to strengthen over the Gulf of
Mexico and there is an increasing risk of dangerous storm surge,
wind, and rainfall impacts along portions of the U.S. Gulf Coast by
the middle of the week. This could result in a prolonged period of
hazardous weather for areas that are likely to be affected by Marco.
Interests along the Gulf Coast should monitor the progress of Laura
and Marco and updates to the forecast during the next couple of
days.
FORECAST POSITIONS AND MAX WINDS
INIT 24/0900Z 20.8N 78.9W 55 KT 65 MPH
12H 24/1800Z 21.7N 81.5W 55 KT 65 MPH
24H 25/0600Z 22.9N 84.6W 60 KT 70 MPH
36H 25/1800Z 24.5N 87.6W 65 KT 75 MPH
48H 26/0600Z 26.1N 90.2W 75 KT 85 MPH
60H 26/1800Z 28.0N 92.3W 85 KT 100 MPH
72H 27/0600Z 29.8N 93.3W 90 KT 105 MPH
96H 28/0600Z 35.4N 91.5W 35 KT 40 MPH...INLAND
120H 29/0600Z 37.6N 82.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
$$
Forecaster Stewart
Tropical Storm Laura Advisory Number 18
NWS National Hurricane Center Miami FL AL132020
500 AM EDT Mon Aug 24 2020
...TROPICAL STORM WARNING ISSUED FOR PORTIONS OF THE FLORIDA KEYS...
...HEAVY RAINFALL OVER EASTERN CUBA AND JAMAICA WILL SPREAD
WESTWARD ACROSS CENTRAL CUBA AND THE CAYMAN ISLANDS TODAY....
SUMMARY OF 500 AM EDT...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...20.8N 78.9W
ABOUT 175 MI...285 KM ESE OF CAYO LARGO
ABOUT 255 MI...415 KM ESE OF THE ISLE OF YOUTH
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 21 MPH...33 KM/H
MINIMUM CENTRAL PRESSURE...1000 MB...29.53 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:
A Tropical Storm Warning has been issued for the middle and lower
Florida Keys from Craig Key westward to Key West.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT:
A Tropical Storm Warning is in effect for...
* Little Cayman and Cayman Brac
* Cuban provinces of Camaguey, Las Tunas, Holguin, Guantanamo,
Santiago de Cuba, Granma, 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
The Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area, in this case within the
next 12 to 24 hours.
A Hurricane Watch will likely be required for portions of the U.S.
northwest Gulf coast area by this evening.
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 AM EDT (0900 UTC), the center of Tropical Storm Laura was
located near latitude 20.8 North, longitude 78.9 West. Laura is
moving toward the west-northwest near 21 mph (33 km/h), and this
general motion with some decrease in forward speed is expected over
the next couple of days. A turn toward the northwest is forecast by
Wednesday. On the forecast track, the center of Laura will move
over the Caribbean Sea just offshore the southern coast of Cuba
today, and move into the southeastern Gulf of Mexico by early
Tuesday morning. Laura is then forecast to move over the central and
northwestern Gulf of Mexico Tuesday night and Wednesday.
Maximum sustained winds are near 65 mph (100 km/h) with higher
gusts. Gradual strengthening is expected, and Laura is forecast to
become a hurricane by early Tuesday.
Tropical-storm-force winds extend outward up to 175 miles (280 km)
from the center.
The estimated minimum central pressure is 1000 mb (29.53 inches).
HAZARDS AFFECTING LAND
----------------------
RAINFALL: Laura is expected to produce the following storm total
rainfall accumulations through Tuesday:
Jamaica and Cuba: 4 to 8 inches, with maximum amounts of 12 inches.
Cayman Islands: 2 to 4 inches, maximum amounts of 6 inches.
Florida Keys, Turks and Caicos Islands, and the Northwest Bahamas:
1 to 2 inches.
Across the Greater Antilles this heavy rainfall could lead to
life-threatening flash and urban flooding, and the potential for
mudslides.
From late Wednesday into Friday, Laura is expected to produce
rainfall of 5 to 10 inches, with isolated maximum amounts of 15
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 the
possibility of some minor river flooding across this region.
WIND: Tropical storm conditions are expected to spread westward
within the warning area in Cuba through today. Tropical storm
conditions are expected in Little Cayman and Cayman Brac by this
afternoon. Tropical storm conditions are also expected within
the warning area in the Florida middle and Lower Keys and the Dry
Tortugas this afternoon and continuing into tonight.
SURF: Swells generated by Laura are affecting portions of
Hispaniola, eastern Cuba, the southeastern Bahamas and the
Turks and Caicos Islands. These swells are expected to spread
across central and western Cuba, the central and northwestern
Bahamas, and the Florida Keys today. Please consult products
from your local weather office.
TORNADOES: An isolated tornado will be possible later today into
tonight across the Florida Keys.
NEXT ADVISORY
-------------
Next intermediate advisory at 800 AM EDT.
Next complete advisory at 1100 AM EDT.
$$
Forecaster Stewart
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