Potential Tropical Cyclone Nine Advisory 6

1. Potential Tropical Cyclone Nine will produce heavy rains and potentially life-threatening flash flooding and mudslides across the northern Leeward Islands, the Virgin Islands, Puerto Rico, the Dominican Republic, northern Haiti, and over the Inagua Islands into the southeastern Bahamas. 2. Tropical storm conditions are likely across portions of the Leeward Islands, the Virgin Islands, and Puerto Rico through tonight and will spread westward to portions of the Dominican Republic, Haiti, and the southeastern Bahamas and Turks and Caicos on Thursday and Thursday night. Tropical Storm Warnings are in effect for these areas. Do not focus on the details of the track forecast, as rainfall and wind hazards will extend far from the center of the system.

3. The details of the long-range track and intensity forecasts remain more uncertain than usual since the system does not have a well-defined center and it is expected to move near or over portions of the Greater Antilles later this week and move near or over Florida this weekend. While this system could bring some rainfall and wind impacts to portions of Cuba, the central and northwest Bahamas, and Florida later this week and this weekend, it is too soon to determine the location or magnitude of those impacts. Interests there should monitor the progress of this system and updates to the forecast over the next few days.

1. Potential Tropical Cyclone Nine will produce heavy rains and potentially life-threatening flash flooding and mudslides across the northern Leeward Islands, the Virgin Islands, Puerto Rico, the Dominican Republic, northern Haiti, and over the Inagua Islands into the southeastern Bahamas. 2. Tropical storm conditions are likely across portions of the Leeward Islands, the Virgin Islands, and Puerto Rico through tonight and will spread westward to portions of the Dominican Republic, Haiti, and the southeastern Bahamas and Turks and Caicos on Thursday and Thursday night. Tropical Storm Warnings are in effect for these areas. Do not focus on the details of the track forecast, as rainfall and wind hazards will extend far from the center of the system.

3. The details of the long-range track and intensity forecasts remain more uncertain than usual since the system does not have a well-defined center and it is expected to move near or over portions of the Greater Antilles later this week and move near or over Florida this weekend. While this system could bring some rainfall and wind impacts to portions of Cuba, the central and northwest Bahamas, and Florida later this week and this weekend, it is too soon to determine the location or magnitude of those impacts. Interests there should monitor the progress of this system and updates to the forecast over the next few days.

CHANGES WITH THIS ADVISORY:

The government of Antigua has discontinued the Tropical Storm Warning for Montserrat, St. Kitts, and Nevis.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Warning is in effect for...
- Puerto Rico, Vieques, Culebra
- U.S. Virgin Islands
- British Virgin Islands
- Anguilla
- St. Martin and St. Barthelemy
- Saba and St. Eustatius
- St. Maarten
- Dominican Republic entire southern and northern coastlines
- North coast of Haiti from Le Mole St Nicholas eastward to the northern border with the Dominican Republic
- Turks and Caicos Islands
- Southeastern Bahamas including the Acklins, Crooked Island, Long Cay, the Inaguas, Mayaguana, and the Ragged Islands

A Tropical Storm Watch is in effect for...
- Central Bahamas, including Cat Island, the Exumas, Long Island, Rum Cay, and San Salvador

Interests in the northwestern Bahamas and Cuba should monitor the progress of this system.

A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours.

A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours.

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.

CHANGES WITH THIS ADVISORY:

The government of Antigua has discontinued the Tropical Storm Warning for Montserrat, St. Kitts, and Nevis.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Warning is in effect for...
- Puerto Rico, Vieques, Culebra
- U.S. Virgin Islands
- British Virgin Islands
- Anguilla
- St. Martin and St. Barthelemy
- Saba and St. Eustatius
- St. Maarten
- Dominican Republic entire southern and northern coastlines
- North coast of Haiti from Le Mole St Nicholas eastward to the northern border with the Dominican Republic
- Turks and Caicos Islands
- Southeastern Bahamas including the Acklins, Crooked Island, Long Cay, the Inaguas, Mayaguana, and the Ragged Islands

A Tropical Storm Watch is in effect for...
- Central Bahamas, including Cat Island, the Exumas, Long Island, Rum Cay, and San Salvador

Interests in the northwestern Bahamas and Cuba should monitor the progress of this system.

A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours.

A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours.

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.

Key messages for Potential Tropical Cyclone Nine can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT4, WMO header WTNT44 KNHC, and on the web at www.hurricanes.gov/text/MIATCDAT4.shtml.

WIND: Tropical storm conditions will continue across portions of the Leeward Islands, the U.S. and British Virgin Islands and Puerto Rico through tonight. These conditions are forecast to reach portions of the Dominican Republic and Haiti within the warning area by late tonight or early Thursday, and the southeastern Bahamas and Turks and Caicos Thursday afternoon. Tropical storm conditions are possible in the watch area on Friday.

RAINFALL: The disturbance is expected to produce the following rain accumulations: Across the northern Leeward Islands, British and U.S. Virgin Islands: 3 to 6 inches. Across Puerto Rico: 3 to 6 inches, with isolated maximum totals of 10 inches. Across the Dominican Republic, northern Haiti, and Turks and Caicos: 3 to 6 inches, with isolated maximum totals of 8 inches. Across the Inagua Islands and southeastern Bahamas: 4 to 8 inches. These rainfall amounts may lead to lifethreatening flash flooding and mudslides, as well as potential riverine flooding beginning today. Urban and small stream flooding is expected for the U.S. Virgin Islands and eastern Puerto Rico.

SURF: Swells generated by Potential Tropical Cyclone Nine will be affecting portions of the Leeward Islands, the Virgin Islands and Puerto Rico through Thursday. These swells are forecast to reach the north coast of the Dominican Republic, the Turks and Caicos Islands and the southeastern Bahamas tonight or Thursday. These swells are likely to cause lifethreatening surf and rip current conditions. Please consult products from your local weather office.

Key messages for Potential Tropical Cyclone Nine can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT4, WMO header WTNT44 KNHC, and on the web at www.hurricanes.gov/text/MIATCDAT4.shtml.

WIND: Tropical storm conditions will continue across portions of the Leeward Islands, the U.S. and British Virgin Islands and Puerto Rico through tonight. These conditions are forecast to reach portions of the Dominican Republic and Haiti within the warning area by late tonight or early Thursday, and the southeastern Bahamas and Turks and Caicos Thursday afternoon. Tropical storm conditions are possible in the watch area on Friday.

RAINFALL: The disturbance is expected to produce the following rain accumulations: Across the northern Leeward Islands, British and U.S. Virgin Islands: 3 to 6 inches. Across Puerto Rico: 3 to 6 inches, with isolated maximum totals of 10 inches. Across the Dominican Republic, northern Haiti, and Turks and Caicos: 3 to 6 inches, with isolated maximum totals of 8 inches. Across the Inagua Islands and southeastern Bahamas: 4 to 8 inches. These rainfall amounts may lead to lifethreatening flash flooding and mudslides, as well as potential riverine flooding beginning today. Urban and small stream flooding is expected for the U.S. Virgin Islands and eastern Puerto Rico.

SURF: Swells generated by Potential Tropical Cyclone Nine will be affecting portions of the Leeward Islands, the Virgin Islands and Puerto Rico through Thursday. These swells are forecast to reach the north coast of the Dominican Republic, the Turks and Caicos Islands and the southeastern Bahamas tonight or Thursday. These swells are likely to cause lifethreatening surf and rip current conditions. Please consult products from your local weather office.

At 500 PM AST (2100 UTC), the disturbance was centered near latitude 16.4 North, longitude 65.6 West. The system is moving toward the westnorthwest near 23 mph (37 km/h), and this general motion with a reduction in forward speed is expected over the next few days. On the forecast track, the system will pass south of Puerto Rico later tonight, near or over Hispaniola on Thursday, near eastern Cuba and the southeastern Bahamas on Friday, and approach the northwestern Bahamas and southern Florida Friday night.

Maximum sustained winds are near 45 mph (75 km/h) with higher gusts. Some increase in strength is forecast through tonight, with weakening likely on Thursday due to land interaction. Some restrengthening is possible by this weekend. Environmental conditions are expected to be conducive for additional development, and a tropical storm is forecast to form tonight. * Formation chance through 48 hours...high...90 percent * Formation chance through 5 days...high...90 percent

Tropicalstormforce winds extend outward up to 275 miles (445 km) primarily to the north of the center. A wind gust of 52 mph (83 km/h) was recently reported at St. Thomas in the U.S. Virgin Islands.

The estimated minimum central pressure is 1004 mb (29.65 inches).

At 500 PM AST (2100 UTC), the disturbance was centered near latitude 16.4 North, longitude 65.6 West. The system is moving toward the westnorthwest near 23 mph (37 km/h), and this general motion with a reduction in forward speed is expected over the next few days. On the forecast track, the system will pass south of Puerto Rico later tonight, near or over Hispaniola on Thursday, near eastern Cuba and the southeastern Bahamas on Friday, and approach the northwestern Bahamas and southern Florida Friday night.

Maximum sustained winds are near 45 mph (75 km/h) with higher gusts. Some increase in strength is forecast through tonight, with weakening likely on Thursday due to land interaction. Some restrengthening is possible by this weekend. Environmental conditions are expected to be conducive for additional development, and a tropical storm is forecast to form tonight. * Formation chance through 48 hours...high...90 percent * Formation chance through 5 days...high...90 percent

Tropicalstormforce winds extend outward up to 275 miles (445 km) primarily to the north of the center. A wind gust of 52 mph (83 km/h) was recently reported at St. Thomas in the U.S. Virgin Islands.

The estimated minimum central pressure is 1004 mb (29.65 inches).

Deep convection has continued to increase in association with the disturbance since the previous advisory. More recently, a band has developed over the southwestern portion of the broad circulation and it appears that the system may be closer to acquiring a well-defined center. Earlier ASCAT data that arrived shortly after the release of the previous advisory revealed a large area of 35-40 kt winds well to the north of the vorticity maximum. This supports maintaining the initial intensity of 40 kt.

The estimated motion remains a brisk 290/20 kt. A strong subtropical ridge that extends westward over the western Atlantic should continue to steer the system west-northwestward over the next couple of days, bringing the system near or over Hispaniola late tonight and Thursday. A mid-latitude trough moving into the central United States on Friday is foreast to weaken the western portion of the ridge which should cause a reduction in the forward speed of the system and a turn toward the northwest and north later in the forecast period. The latest iterations of the dynamical models have trended toward a more eastward solution, taking the system near or just east of the Florida peninsula. Since the system still lacks a well-defined center it is not surprising to see these inconsistencies in the model runs. As a result, the NHC forecast has been shifted eastward, but it remains to the west of the latest multi-model consensus aids out of respect for continuity and the continued possibility of further model shifts.

The system is still forecast to become a tropical storm before reaching Hispaniola, and some slight strengthening could occur before landfall Thursday morning. Some weakening is likely as the system moves over that island. The system is likely to take some time to recover after its passage over land, and given the forecast for at least moderate south to southwesterly shear, only gradual strengthening is indicated at that time. As mentioned above, some of the global models are now showing a track farther away from eastern Cuba and east of Florida, and if that occurs the NHC intensity forecast could be somewhat conservative. Interests in the Bahamas, Cuba, and Florida should continue to monitor forecasts as changes to both the track and intensity are likely.

Deep convection has continued to increase in association with the disturbance since the previous advisory. More recently, a band has developed over the southwestern portion of the broad circulation and it appears that the system may be closer to acquiring a well-defined center. Earlier ASCAT data that arrived shortly after the release of the previous advisory revealed a large area of 35-40 kt winds well to the north of the vorticity maximum. This supports maintaining the initial intensity of 40 kt.

The estimated motion remains a brisk 290/20 kt. A strong subtropical ridge that extends westward over the western Atlantic should continue to steer the system west-northwestward over the next couple of days, bringing the system near or over Hispaniola late tonight and Thursday. A mid-latitude trough moving into the central United States on Friday is foreast to weaken the western portion of the ridge which should cause a reduction in the forward speed of the system and a turn toward the northwest and north later in the forecast period. The latest iterations of the dynamical models have trended toward a more eastward solution, taking the system near or just east of the Florida peninsula. Since the system still lacks a well-defined center it is not surprising to see these inconsistencies in the model runs. As a result, the NHC forecast has been shifted eastward, but it remains to the west of the latest multi-model consensus aids out of respect for continuity and the continued possibility of further model shifts.

The system is still forecast to become a tropical storm before reaching Hispaniola, and some slight strengthening could occur before landfall Thursday morning. Some weakening is likely as the system moves over that island. The system is likely to take some time to recover after its passage over land, and given the forecast for at least moderate south to southwesterly shear, only gradual strengthening is indicated at that time. As mentioned above, some of the global models are now showing a track farther away from eastern Cuba and east of Florida, and if that occurs the NHC intensity forecast could be somewhat conservative. Interests in the Bahamas, Cuba, and Florida should continue to monitor forecasts as changes to both the track and intensity are likely.

al092020 Potential Tropical Cyclone Nine