2. Shower activity associated with a tropical wave located about 800
miles southwest of the Cabo Verde islands has become a little
better organized since yesterday. Additional slow development of
this system is possible during the next several days as it moves
generally west-northwestward at about 20 mph.
* Formation chance through 48 hours...low...10 percent.
* Formation chance through 5 days...low...20 percent.
1. A broad area of low pressure, associated with a tropical wave, is
located about midway between the west coast of Africa and the
Windward Islands. This system is producing a large area of showers
and thunderstorms that are starting to show some signs of
organization. Environmental conditions appear generally favorable
for development, and a tropical depression could form during the
next few days while the system moves west-northwestward at about 20
mph. Interests in the Windward and Leeward Islands should closely
monitor this system as it will likely be moving through that region
on Friday.
* Formation chance through 48 hours...medium...40 percent.
* Formation chance through 5 days...medium...60 percent.
1. Showers and thunderstorms associated with a broad low pressure area
and tropical wave located about 1300 miles east-southeast of the
Windward Islands have become better organized since yesterday.
However, recent satellite wind data indicates that the disturbance
does not have a well-defined circulation. Environmental conditions
appear generally favorable for continued development, and a tropical
depression or storm is likely to form during the next day or two
while the system moves west-northwestward at 20 to 25 mph.
Interests in the Lesser Antilles should closely monitor the progress
of this system, as advisories on a potential tropical cyclone,
accompanied by tropical storm watches for portions of this area, are
likely to be issued later today.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...90 percent.
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.
Tropical Depression Five Discussion Number 2
NWS National Hurricane Center Miami FL AL052021
1100 PM AST Wed Jun 30 2021
The satellite presentation of the system over the last 6-12 hours
has continued to gradually improve, with a prominent banding feature
to the west of the estimated center. An ASCAT-A pass received at
2323 UTC revealed that the low-level circulation has become a bit
better defined compared to earlier today, though still somewhat
elongated to the south and west. The peak wind retrievals from this
instrument were 30-32 kt. While subjective satellite estimates
from TAFB and SAB were a bit higher, the latest estimated intensity
was held at 30 kt for this advisory in agreement with the slightly
lower scatterometer data.
The initial motion has accelerated a bit tonight at 280/20
kt. A strong subtropical ridge is situated poleward of the tropical
depression and this feature should steer the system quickly to the
west-northwest over the next several days. After 72 hours, the
tropical cyclone will reach the westward extent of the ridge and
begin to move more poleward and slow down as the ridge also becomes
eroded by a mid-latitude trough to over the eastern US. The track
guidance in the latter portion of the forecast continues to exhibit
large spread, with the GFS and HWRF/HMON models along the left side
of the guidance envelop, while the ECMWF and its ensemble mean
on the right side. The latest NHC track forecast is a shade right
of the previous one, and also slightly faster, but given the spread
in the models, the latter portion of the track is more uncertain
than usual.
While the depression is currently in a favorable environment of low
vertical wind shear, warm sea-surface temperatures, and high
mid-level relative humidity, the expected acceleration in forward
motion could cause the system to outrun the favorable upper-level
easterlies currently overhead, after 36 hours. In addition, the
system could be near or over some of the Greater Antilles in the
latter portions of the forecast. For these reasons, the intensity
remained capped at 50 kt after 36 hours, and is still on the lower
end of the intensity guidance suite, though this forecast could be
somewhat conservative.
Key Messages:
1. The tropical depression is expected to become a tropical storm
before reaching the Lesser Antilles and tropical storm conditions
are expected beginning late Thursday night 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. 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.
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