Potential Tropical Cyclone Seven Advisory Number 1...Corrected
NWS National Hurricane Center Miami FL AL072021
1100 AM AST Fri Aug 13 2021
Corrected to indicate issuance time of intermediate advisory.
...DISTURBANCE OVER THE CENTRAL TROPICAL ATLANTIC EXPECTED TO
BECOME A TROPICAL STORM BY SATURDAY...
...TROPICAL STORM WATCHES ISSUED FOR A PORTION OF THE LEEWARD
ISLANDS...
SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...15.3N 49.3W
ABOUT 840 MI...1350 KM E OF THE LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 21 MPH...33 KM/H
MINIMUM CENTRAL PRESSURE...1010 MB...29.83 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:
The government of Antigua and Barbuda has issued a Tropical Storm
Watch for Antigua and Barbuda, St. Kitts and Nevis, and Montserrat.
The government of the Netherlands has issued a Tropical Storm Watch
for Saba and Sint Eustatius.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT:
A Tropical Storm Watch is in effect for...
* Antigua and Barbuda, St. Kitts and Nevis, and Montserrat
* Saba and Sint Eustatius
A Tropical Storm Watch means that tropical storm conditions are
possible within the watch area, generally within 48 hours.
Interests elsewhere in the Leeward Islands, the Virgin Islands, and
Puerto Rico should monitor the progress of this system. Tropical
Storm Watches will likely be required for these areas later today
or tonight.
For storm information specific to your area, please monitor
products issued by your national meteorological service.
DISCUSSION AND OUTLOOK
----------------------
At 1100 AM AST (1500 UTC), the disturbance was centered near
latitude 15.3 North, longitude 49.3 West. The system is moving
toward the west near 21 mph (33 km/h), and this general motion with
a gradual decrease in forward speed is expected into early next
week. On the forecast track, the system is expected to approach
the Leeward Islands on Saturday, move over the Leeward Islands
Saturday night and Sunday, and then be near the Virgin Islands and
Puerto Rico Sunday night and Monday.
Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Gradual strengthening is forecast during the next couple of days,
and the disturbance is expected to become a tropical depression
tonight and a tropical storm by Saturday.
* Formation chance through 48 hours...high...80 percent.
* Formation chance through 5 days...high...80 percent.
The estimated minimum central pressure is 1010 mb (29.83 inches).
HAZARDS AFFECTING LAND
----------------------
Key messages for Potential Tropical Cyclone Seven can be found in
the Tropical Cyclone Discussion under AWIPS header MIATCDAT2 and
WMO header WTNT42 KNHC and on the web at
www.hurricanes.gov/graphics_at2.shtml?key_messages.
WIND: Tropical storm conditions are possible within the watch
area by Saturday night or early Sunday.
RAINFALL: The system is expected to produce rainfall of 3 to 6
inches across the northern Leeward Islands Saturday into Sunday.
This rainfall may produce scattered areas of flash flooding.
NEXT ADVISORY
-------------
Next intermediate advisory at 200 PM AST.
Next complete advisory at 500 PM AST.
$$
Forecaster Berg/Brennan
Potential Tropical Cyclone Seven Discussion Number 1
NWS National Hurricane Center Miami FL AL072021
1100 AM AST Fri Aug 13 2021
A tropical wave and small area of low pressure moving quickly
westward across the central tropical Atlantic has been producing
bursts of deep convection near and to the west of the wave axis.
Scatterometer data from last evening indicated that the system did
not quite have a closed circulation, but it is close. In addition,
the convective organization has increased a bit since yesterday,
with TAFB and SAB providing Dvorak classification of T1.5 and T2.0.
Therefore, only an additional slight increase in convective
organization and the low-level circulation closing off would make
the system a tropical depression, and it could be at tropical storm
strength when it approaches the Leeward Islands during the next
couple of days. Therefore, advisories are being initiated on the
system in order to issue Tropical Storm Watches for portions of the
Leeward Islands at this time.
Subtropical ridging extending across nearly the entire Atlantic is
pushing the low along quickly toward the west, or 280/18 kt. In
general this ridging is expected to persist into the middle part of
next week. However, around the Sunday-Monday time frame, some
mid-level troughing over the western Atlantic could allow the
system to gain a little more latitude before it runs into
additional ridging located near the east coast of the United States
at the end of the forecast period. The GFS, which has perhaps one
of the strongest solutions, is a northern outlier and shows the
system turning farther into the weak troughing, while the ECMWF has
a weaker solution and keeps the system on a westward track across
the Lesser and Greater Antilles. At this time, the NHC official
forecast lies close to the TVCN and HCCA consensus aids, and it is
also relatively close to the ECMWF ensemble mean, which is farther
north than its parent model.
The biggest negative to the system becoming a tropical cyclone and
strengthening is its fast motion of 15-20 kt. However, that motion
is expected to gradually decrease in 2 to 3 days. At that same
time, deep-layer shear has decreased a bit, and the system will be
moving over warmer waters and toward a slightly more moist
environment. Therefore, gradual strengthening is anticipated, and
the NHC intensity forecast closely follows the HCCA and IVCN
consensus aids through 72 hours, up until the system is near
Hispaniola. After that time, land interaction is likely to disrupt
the circulation, and the official forecast is below the model
consensus aids on days 4 and 5.
Key Messages:
1. Tropical storm conditions are possible in portions of the
Leeward Islands late Saturday or early Sunday, and the risk of
tropical storm conditions will spread westward to the Virgin
Islands and Puerto Rico late Sunday and Sunday night.
2. Heavy rainfall with this system may produce areas of scattered
flash flooding over the northern Leeward Islands Saturday into
Sunday.
3. There is a risk of wind and rainfall impacts in portions of
Hispaniola, the Turks and Caicos Islands, the southeastern Bahamas,
and Cuba next week, and interests in those areas should monitor the
progress of this system.
FORECAST POSITIONS AND MAX WINDS
INIT 13/1500Z 15.3N 49.3W 30 KT 35 MPH...POTENTIAL TROP CYCLONE
12H 14/0000Z 15.7N 52.0W 30 KT 35 MPH...TROPICAL DEPRESSION
24H 14/1200Z 16.2N 55.9W 35 KT 40 MPH
36H 15/0000Z 16.7N 59.6W 35 KT 40 MPH
48H 15/1200Z 17.2N 63.0W 40 KT 45 MPH
60H 16/0000Z 17.8N 66.0W 40 KT 45 MPH
72H 16/1200Z 18.4N 68.7W 45 KT 50 MPH...OVER HISPANIOLA
96H 17/1200Z 20.0N 73.5W 35 KT 40 MPH...OVER WATER
120H 18/1200Z 23.0N 77.0W 40 KT 45 MPH
$$
Forecaster Berg
NWS National Hurricane Center Miami FL AL072021
1100 AM AST Fri Aug 13 2021
Corrected to indicate issuance time of intermediate advisory.
...DISTURBANCE OVER THE CENTRAL TROPICAL ATLANTIC EXPECTED TO
BECOME A TROPICAL STORM BY SATURDAY...
...TROPICAL STORM WATCHES ISSUED FOR A PORTION OF THE LEEWARD
ISLANDS...
SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...15.3N 49.3W
ABOUT 840 MI...1350 KM E OF THE LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 21 MPH...33 KM/H
MINIMUM CENTRAL PRESSURE...1010 MB...29.83 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:
The government of Antigua and Barbuda has issued a Tropical Storm
Watch for Antigua and Barbuda, St. Kitts and Nevis, and Montserrat.
The government of the Netherlands has issued a Tropical Storm Watch
for Saba and Sint Eustatius.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT:
A Tropical Storm Watch is in effect for...
* Antigua and Barbuda, St. Kitts and Nevis, and Montserrat
* Saba and Sint Eustatius
A Tropical Storm Watch means that tropical storm conditions are
possible within the watch area, generally within 48 hours.
Interests elsewhere in the Leeward Islands, the Virgin Islands, and
Puerto Rico should monitor the progress of this system. Tropical
Storm Watches will likely be required for these areas later today
or tonight.
For storm information specific to your area, please monitor
products issued by your national meteorological service.
DISCUSSION AND OUTLOOK
----------------------
At 1100 AM AST (1500 UTC), the disturbance was centered near
latitude 15.3 North, longitude 49.3 West. The system is moving
toward the west near 21 mph (33 km/h), and this general motion with
a gradual decrease in forward speed is expected into early next
week. On the forecast track, the system is expected to approach
the Leeward Islands on Saturday, move over the Leeward Islands
Saturday night and Sunday, and then be near the Virgin Islands and
Puerto Rico Sunday night and Monday.
Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Gradual strengthening is forecast during the next couple of days,
and the disturbance is expected to become a tropical depression
tonight and a tropical storm by Saturday.
* Formation chance through 48 hours...high...80 percent.
* Formation chance through 5 days...high...80 percent.
The estimated minimum central pressure is 1010 mb (29.83 inches).
HAZARDS AFFECTING LAND
----------------------
Key messages for Potential Tropical Cyclone Seven can be found in
the Tropical Cyclone Discussion under AWIPS header MIATCDAT2 and
WMO header WTNT42 KNHC and on the web at
www.hurricanes.gov/graphics_at2.shtml?key_messages.
WIND: Tropical storm conditions are possible within the watch
area by Saturday night or early Sunday.
RAINFALL: The system is expected to produce rainfall of 3 to 6
inches across the northern Leeward Islands Saturday into Sunday.
This rainfall may produce scattered areas of flash flooding.
NEXT ADVISORY
-------------
Next intermediate advisory at 200 PM AST.
Next complete advisory at 500 PM AST.
$$
Forecaster Berg/Brennan
Potential Tropical Cyclone Seven Discussion Number 1
NWS National Hurricane Center Miami FL AL072021
1100 AM AST Fri Aug 13 2021
A tropical wave and small area of low pressure moving quickly
westward across the central tropical Atlantic has been producing
bursts of deep convection near and to the west of the wave axis.
Scatterometer data from last evening indicated that the system did
not quite have a closed circulation, but it is close. In addition,
the convective organization has increased a bit since yesterday,
with TAFB and SAB providing Dvorak classification of T1.5 and T2.0.
Therefore, only an additional slight increase in convective
organization and the low-level circulation closing off would make
the system a tropical depression, and it could be at tropical storm
strength when it approaches the Leeward Islands during the next
couple of days. Therefore, advisories are being initiated on the
system in order to issue Tropical Storm Watches for portions of the
Leeward Islands at this time.
Subtropical ridging extending across nearly the entire Atlantic is
pushing the low along quickly toward the west, or 280/18 kt. In
general this ridging is expected to persist into the middle part of
next week. However, around the Sunday-Monday time frame, some
mid-level troughing over the western Atlantic could allow the
system to gain a little more latitude before it runs into
additional ridging located near the east coast of the United States
at the end of the forecast period. The GFS, which has perhaps one
of the strongest solutions, is a northern outlier and shows the
system turning farther into the weak troughing, while the ECMWF has
a weaker solution and keeps the system on a westward track across
the Lesser and Greater Antilles. At this time, the NHC official
forecast lies close to the TVCN and HCCA consensus aids, and it is
also relatively close to the ECMWF ensemble mean, which is farther
north than its parent model.
The biggest negative to the system becoming a tropical cyclone and
strengthening is its fast motion of 15-20 kt. However, that motion
is expected to gradually decrease in 2 to 3 days. At that same
time, deep-layer shear has decreased a bit, and the system will be
moving over warmer waters and toward a slightly more moist
environment. Therefore, gradual strengthening is anticipated, and
the NHC intensity forecast closely follows the HCCA and IVCN
consensus aids through 72 hours, up until the system is near
Hispaniola. After that time, land interaction is likely to disrupt
the circulation, and the official forecast is below the model
consensus aids on days 4 and 5.
Key Messages:
1. Tropical storm conditions are possible in portions of the
Leeward Islands late Saturday or early Sunday, and the risk of
tropical storm conditions will spread westward to the Virgin
Islands and Puerto Rico late Sunday and Sunday night.
2. Heavy rainfall with this system may produce areas of scattered
flash flooding over the northern Leeward Islands Saturday into
Sunday.
3. There is a risk of wind and rainfall impacts in portions of
Hispaniola, the Turks and Caicos Islands, the southeastern Bahamas,
and Cuba next week, and interests in those areas should monitor the
progress of this system.
FORECAST POSITIONS AND MAX WINDS
INIT 13/1500Z 15.3N 49.3W 30 KT 35 MPH...POTENTIAL TROP CYCLONE
12H 14/0000Z 15.7N 52.0W 30 KT 35 MPH...TROPICAL DEPRESSION
24H 14/1200Z 16.2N 55.9W 35 KT 40 MPH
36H 15/0000Z 16.7N 59.6W 35 KT 40 MPH
48H 15/1200Z 17.2N 63.0W 40 KT 45 MPH
60H 16/0000Z 17.8N 66.0W 40 KT 45 MPH
72H 16/1200Z 18.4N 68.7W 45 KT 50 MPH...OVER HISPANIOLA
96H 17/1200Z 20.0N 73.5W 35 KT 40 MPH...OVER WATER
120H 18/1200Z 23.0N 77.0W 40 KT 45 MPH
$$
Forecaster Berg
