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Tropical Storm Laura Discussion Number 9
NWS National Hurricane Center Miami FL AL132020
1100 PM AST Fri Aug 21 2020
Laura remains quite disorganized this evening. Although satellite
and radar images show a fair amount of deep convection over and to
the east of the northern Leeward Islands, NOAA Hurricane
Hunter data and surface observations indicate that the low-level
center is located well to the west of the main area of deep
convection. This asymmetric structure indicates that Laura is still
not vertically aligned due to at least moderate wind shear. The
initial intensity is held at a possibly generous 40 kt, and most of
the strongest winds are well north and east of the center.
The steering pattern for Laura appears to be very well established.
A subtropical ridge over the central and western Atlantic is
expected to expand westward, and that should cause Laura to move
west-northwestward at a fairly quick pace during the next few days.
This should take the storm across Puerto Rico on Saturday, near
Hispaniola Saturday night, and close to or over Cuba on Sunday and
Monday. By early next week, Laura should approach the western end
of the ridge and that should cause the storm to slow down and turn
toward the northwest over the eastern and central Gulf of Mexico.
Even though the steering pattern is well established, there are
still chances of center reformations, which could cause small but
important track changes. The NHC track forecast has been adjusted
a little to the south of the previous one to account for the more
southern initial position and westward motion. Near the end of the
period, Laura's track could also be influenced by Tropical Storm
Marco, which is also forecast to be over the Gulf of Mexico,
however the details of that interaction are highly uncertain
at this time.
Although the storm's structure is quite ragged at the moment, some
of the models do show Laura becoming better organized this
weekend and early next week due to a decrease in wind shear and
very warm waters. However, there is significant uncertainty on how
much the circulation will interact with the rugged islands of
Hispaniola and Cuba. If the storm is able to stay north of those
islands, some notable strengthening is possible as depicted by the
HWRF and HMON models. However, if the storm moves over the
islands, it might not strengthen at all until it passes through
that area. The bottom line is the intensity forecast is very
track dependent, which makes it more uncertain than normal. Given
that the new track shows more land interaction, this forecast shows
less strengthening in the short term, but is largely unchanged at
the longer forecast times.
1. Tropical storm conditions are expected across portions of the
northern Leeward Islands, the Virgin Islands, and Puerto Rico
through Saturday. Tropical storm conditions are also expected along
the northern coasts of the Dominican Republic and Haiti, and the
Turks and Caicos and southeastern Bahamas Saturday into Sunday.
Heavy rainfall is likely across these areas beginning and could
cause mudslides and flash and urban flooding through Sunday.
2. Tropical storm conditions are possible over portions of the
central Bahamas Sunday night.
3. The details of the long-range track and intensity forecasts
remain more uncertain than usual since Laura is forecast to move
near or over portions of the Greater Antilles through Monday.
However, Laura could bring storm surge, rainfall, and wind impacts
to portions of Cuba, the Bahamas, and Florida early next week and
the northern U.S. Gulf Coast by the middle of next week. Interests
there should monitor the progress of Laura and updates to the
forecast during the next few days.
FORECAST POSITIONS AND MAX WINDS
INIT 22/0300Z 17.0N 63.5W 40 KT 45 MPH
12H 22/1200Z 17.6N 65.9W 40 KT 45 MPH
24H 23/0000Z 18.4N 69.3W 40 KT 45 MPH...INLAND
36H 23/1200Z 19.5N 72.8W 40 KT 45 MPH...INLAND
48H 24/0000Z 20.8N 76.4W 45 KT 50 MPH...INLAND
60H 24/1200Z 22.1N 80.1W 45 KT 50 MPH...INLAND
72H 25/0000Z 23.8N 83.3W 55 KT 65 MPH...OVER WATER
96H 26/0000Z 26.5N 87.7W 65 KT 75 MPH...OVER WATER
120H 27/0000Z 29.2N 90.2W 65 KT 75 MPH...OVER WATER