Potential Tropical Cyclone Five Advisory Number 1
NWS National Hurricane Center Miami FL AL052021
500 PM AST Wed Jun 30 2021
...TROPICAL DISTURBANCE IN THE ATLANTIC BECOMING BETTER ORGANIZED...
...TROPICAL STORM WATCHES ISSUED FOR PORTIONS OF THE LESSER
ANTILLES...
SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...9.6N 43.7W
ABOUT 1195 MI...1920 KM E OF THE WINDWARD ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 21 MPH...33 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:
The Meteorological Service of Barbados has issued a Tropical Storm
Watch for Barbados, St. Vincent, and the Grenadines.
The Meteorological Service of St. Lucia has issued a Tropical Storm
Watch for St. Lucia.
The Government of France has issued a Tropical Storm Watch for
Martinique.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT:
A Tropical Storm Watch is in effect for...
* St. Vincent and the Grenadines
* St. Lucia
* Barbados
* Martinique
A Tropical Storm Watch means that tropical storm conditions are
possible within the watch area, generally within 48 hours.
Interests elsewhere in the Windward Islands, Leeward Islands, the
Virgin Islands, Puerto Rico, the Dominican Republic, and Haiti
should monitor the progress of this system. Warnings and
additional watches will likely be required tonight and on Thursday.
For storm information specific to your area, please monitor
products issued by your national meteorological service.
DISCUSSION AND OUTLOOK
----------------------
At 500 PM AST (2100 UTC), the disturbance was centered near latitude
9.6 North, longitude 43.7 West. The system is moving toward the
west-northwest near 21 mph (33 km/h) and this motion is expected to
continue with an increase in forward speed during the next couple
of days. On the forecast track, the system will pass near or over
portions of the Windward Islands or the southern Leeward Islands on
Friday, move into the eastern Caribbean Sea late Friday and Friday
night, and move near the southern coast of Hispaniola on Saturday.
Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Some strengthening is forecast during the next 48 hours and the
disturbance is expected to become a tropical storm tonight or on
Thursday.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...90 percent.
The estimated minimum central pressure is 1008 mb (29.77 inches).
HAZARDS AFFECTING LAND
----------------------
Key messages for Potential Tropical Cyclone Five can be found in
the Tropical Cyclone Discussion under AWIPS header MIATCDAT5, WMO
header WTNT45 KNHC and on the web at
http://www.hurricanes.gov/graphics_at5. ... y_messages.
WIND: Tropical-storm conditions are possible in portions of
the Windward and southern Leeward Islands on Friday.
RAINFALL: The potential tropical cyclone will produce rainfall
totals of 3 to 6 inches with maximum totals of 8 inches on Friday
across the Windward and southern Leeward Islands, including
Barbados. This rain may produce isolated flash flooding and
mudslides.
NEXT ADVISORY
-------------
Next intermediate advisory at 800 PM AST.
Next complete advisory at 1100 PM AST.
$$
Forecaster Beven
Potential Tropical Cyclone Five Discussion Number 1
NWS National Hurricane Center Miami FL AL052021
500 PM AST Wed Jun 30 2021
Satellite imagery indicates that the convection associated with the
low pressure area over the central tropical Atlantic is becoming
better organized. However, earlier scatterometer data showed that
the circulation was elongated and not well defined. Since the
system is about 48 h away from the Lesser Antilles and is expected
to become a tropical storm before reaching the islands, advisories
are being initiated at this time on Potential Tropical Cyclone Five.
The initial intensity is set to 30 kt based on the scatterometer
data and satellite intensity estimates from TAFB and SAB.
The initial motion is 285/18. The disturbance is currently on the
south side of a strong subtropical ridge, and for the next 72 h the
system should move rapidly west-northwestward. Indeed, the forward
speed may exceed 25 kt as the system moves through the Lesser
Antilles. There is excellent agreement in the guidance on this
part of the forecast track. After 72 h, the system is expected to
approach a weakness in the ridge caused by a mid-latitude trough
over the eastern United States. The should cause the system to slow
its forward speed and turn more northwestward. The track guidance
become more diverse during this time in regards to how far north
the system will turn, and this part of the NHC forecast track is
most similar to the GFS and UKMET forecasts. Note that the track
forecast is more uncertain than usual since the system does not yet
have a well-defined center.
The disturbance is currently in a favorable upper-level wind
pattern. However, most Atlantic systems in this area moving near 25
kt have trouble strengthening, and there are indications that the
fast forward speed may produce some westerly shear. Thus, the NHC
intensity forecast for the first 72 h is near the lower edge of the
intensity guidance. After 72 h, the intensity forecast becomes
highly uncertain due to possible land interaction and differences in
the model forecasts of the upper-level winds. This portion of the
NHC intensity forecast maintains a constant 50-kt intensity due to
the level of uncertainty.
Key Messages:
1. The system is expected to become a tropical storm before reaching
the Lesser Antilles and tropical storm conditions are possible
beginning Friday in portions of the Windward and southern Leeward
Islands.
2. Heavy rainfall will move quickly across the Windward and southern
Leeward Islands, including Barbados, on Friday. Isolated flash
flooding and mudslides are possible.
3. There is a risk of wind and rainfall impacts in portions of the
Virgin Islands, Puerto Rico, Hispaniola, Cuba, the Turks and Caicos
and the southeastern Bahamas through early next week, although the
forecast is more uncertain than usual since the system does not have
a well-defined center. Interests in these areas should monitor the
system's progress and updates to the forecast.
4. Interests in Florida should monitor updates to the forecast for
this system, but it is too soon to determine what if any impacts
could occur there next week given the uncertainty in the long-range
forecast.
FORECAST POSITIONS AND MAX WINDS
INIT 30/2100Z 9.6N 43.7W 30 KT 35 MPH...POTENTIAL TROP CYCLONE
12H 01/0600Z 10.2N 46.6W 35 KT 40 MPH...TROPICAL CYCLONE
24H 01/1800Z 11.1N 51.0W 40 KT 45 MPH
36H 02/0600Z 12.4N 56.0W 45 KT 50 MPH
48H 02/1800Z 13.8N 61.2W 45 KT 50 MPH
60H 03/0600Z 15.4N 66.3W 50 KT 60 MPH
72H 03/1800Z 17.0N 70.9W 50 KT 60 MPH
96H 04/1800Z 20.0N 77.0W 50 KT 60 MPH...INLAND
120H 05/1800Z 22.5N 81.5W 50 KT 60 MPH...INLAND
$$
Forecaster Beven