Tropical Storm Isaias Advisory 8

1. Isaias will produce heavy rains and potentially life-threatening flash flooding and mudslides across the Virgin Islands, Puerto Rico, the Dominican Republic, northern Haiti, and over the Bahamas.

2. Tropical storm conditions are likely across portions of the the Virgin Islands, and Puerto Rico through this morning and will spread westward to portions of the Dominican Republic, Haiti, and the Turks and Caicos and the Bahamas later today and Friday. 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. While this system could bring some rainfall and wind impacts to portions of Cuba 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 couple of days.

1. Isaias will produce heavy rains and potentially life-threatening flash flooding and mudslides across the Virgin Islands, Puerto Rico, the Dominican Republic, northern Haiti, and over the Bahamas.

2. Tropical storm conditions are likely across portions of the the Virgin Islands, and Puerto Rico through this morning and will spread westward to portions of the Dominican Republic, Haiti, and the Turks and Caicos and the Bahamas later today and Friday. 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. While this system could bring some rainfall and wind impacts to portions of Cuba 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 couple of days.

CHANGES WITH THIS ADVISORY:

The Tropical Storm Warning for St. Martin, St. Barthelemy, St. Maarten, Saba and St. Eustatius has been discontinued.

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
- 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
- Central Bahamas, including Cat Island, the Exumas, Long Island, Rum Cay, and San Salvador

A Tropical Storm Watch is in effect for...
- Northwestern Bahamas including Andros Island, New Providence, Eleuthera, Abacos Islands, Berry Islands, Grand Bahamas Island, and Bimini

Interests in Cuba and the Florida peninsula 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 Tropical Storm Warning for St. Martin, St. Barthelemy, St. Maarten, Saba and St. Eustatius has been discontinued.

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
- 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
- Central Bahamas, including Cat Island, the Exumas, Long Island, Rum Cay, and San Salvador

A Tropical Storm Watch is in effect for...
- Northwestern Bahamas including Andros Island, New Providence, Eleuthera, Abacos Islands, Berry Islands, Grand Bahamas Island, and Bimini

Interests in Cuba and the Florida peninsula 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 Isaias 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 overnight. These conditions are forecast to reach portions of the Dominican Republic and Haiti within the warning area by this morning, and the southeastern Bahamas and Turks and Caicos this afternoon. Tropical storm conditions are expected in the Central Bahamas beginning Friday morning and are possible in the northwestern Bahamas beginning late Friday.

RAINFALL: Isaias is expected to produce the following rain accumulations: British and U.S. Virgin Islands and Turks and Caicos: 3 to 6 inches. Puerto Rico and northern Haiti: 3 to 6 inches, with isolated maximum totals of 8 inches. Dominican Republic: 4 to 8 inches, with isolated maximum totals of 10 inches. Bahamas: 4 to 8 inches. Cuba: 2 to 4 inches, with isolated maximum totals of 6 inches. These rainfall amounts will 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, eastern Puerto Rico, and Hispaniola.

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

Key messages for Isaias 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 overnight. These conditions are forecast to reach portions of the Dominican Republic and Haiti within the warning area by this morning, and the southeastern Bahamas and Turks and Caicos this afternoon. Tropical storm conditions are expected in the Central Bahamas beginning Friday morning and are possible in the northwestern Bahamas beginning late Friday.

RAINFALL: Isaias is expected to produce the following rain accumulations: British and U.S. Virgin Islands and Turks and Caicos: 3 to 6 inches. Puerto Rico and northern Haiti: 3 to 6 inches, with isolated maximum totals of 8 inches. Dominican Republic: 4 to 8 inches, with isolated maximum totals of 10 inches. Bahamas: 4 to 8 inches. Cuba: 2 to 4 inches, with isolated maximum totals of 6 inches. These rainfall amounts will 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, eastern Puerto Rico, and Hispaniola.

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

At 500 AM AST (0900 UTC), the center of Tropical Storm Isaias was located near latitude 17.2 North, longitude 67.9 West. Isaias is moving toward the northwest near 21 mph (33 km/h), and a westnorthwestward to northwestward motion with some decrease in forward speed is expected over the next couple of days. On the forecast track, the center of Isaias will move over Hispaniola late today and near the Southeastern Bahamas by early Friday.

Maximum sustained winds are near 60 mph (95 km/h) with higher gusts. Little change in strength is anticipated until landfall in Dominican Republic later today, with restrengthening forecast on Friday and Saturday.

Tropicalstormforce winds extend outward up to 415 miles (665 km) from the center. A Weatherflow station in Yabucoa Tanque de Agua reported sustained winds of 52 mph (83 km/h) with a gust to 59 mph (94 km/h).

The estimated minimum central pressure is 1003 mb (29.62 inches).

At 500 AM AST (0900 UTC), the center of Tropical Storm Isaias was located near latitude 17.2 North, longitude 67.9 West. Isaias is moving toward the northwest near 21 mph (33 km/h), and a westnorthwestward to northwestward motion with some decrease in forward speed is expected over the next couple of days. On the forecast track, the center of Isaias will move over Hispaniola late today and near the Southeastern Bahamas by early Friday.

Maximum sustained winds are near 60 mph (95 km/h) with higher gusts. Little change in strength is anticipated until landfall in Dominican Republic later today, with restrengthening forecast on Friday and Saturday.

Tropicalstormforce winds extend outward up to 415 miles (665 km) from the center. A Weatherflow station in Yabucoa Tanque de Agua reported sustained winds of 52 mph (83 km/h) with a gust to 59 mph (94 km/h).

The estimated minimum central pressure is 1003 mb (29.62 inches).

Isaias is sending some mixed signals tonight. The 1-min rapid scan data from GOES-16 indicates that the low-level center is likely displaced west of a very intense burst of deep convection on the northeastern side of the circulation. However, the satellite data also shows increased banding features overnight and a more organized central cloud pattern, with recent hints that perhaps a low-level center is trying to re-form closer to the convection. Radar observations from San Juan show 60-65 kt Doppler wind velocities during the past few hours near 5000 ft, so the initial wind speed is raised to 50 kt.

Model forecasts are showing a complex evolution of the tropical cyclone during the next day or two. There is good agreement that Isaias will move across Hispaniola later today, and its low-level center will likely become disorganized over the high terrain. However, the strong burst of convection currently near Puerto Rico is associated with a mid-level circulation, which should pass along the north coast of Hispaniola later today. Most of the model guidance suggest that this feature will cause the re-development of a surface center over the northern part of the broader system while the mid-level circulation moves close to the southeastern Bahamas. Afterward, the cyclone would then move northwestward until the weekend, and gradually turn northward and northeastward close to the U.S. East Coast into early next week ahead of a mid-latitude trough. The official track forecast is a little to the east of the previous one and close to the NOAA corrected dynamical model consensus. It should be noted that further adjustments to the forecast tracks are indeed possible, especially after Isaias moves north of Hispaniola. The intensity forecast is quite tricky. In the short term, Isaias is expected to move across Hispaniola, as the storm's interaction with the mountainous island should cause some weakening and disruption to the circulation. However, as mentioned before, the models suggest that a new center could form, and the environmental conditions would support gradual intensification. The intensity models have been trending higher, and the official forecast is nudged upward accordingly, now showing a peak intensity of 60 kt when the storm is near the coast of Florida and the Southeast U.S. Coast. It should be noted that there are models that show hurricane strength near the U.S. but, given the large amount of uncertainty, it is preferred to stay on the conservative side for now. We should have a better idea of how strong Isaias will become near the U.S. after reconnaissance aircraft sample the storm and after it passes Hispaniola later today.

Isaias is sending some mixed signals tonight. The 1-min rapid scan data from GOES-16 indicates that the low-level center is likely displaced west of a very intense burst of deep convection on the northeastern side of the circulation. However, the satellite data also shows increased banding features overnight and a more organized central cloud pattern, with recent hints that perhaps a low-level center is trying to re-form closer to the convection. Radar observations from San Juan show 60-65 kt Doppler wind velocities during the past few hours near 5000 ft, so the initial wind speed is raised to 50 kt.

Model forecasts are showing a complex evolution of the tropical cyclone during the next day or two. There is good agreement that Isaias will move across Hispaniola later today, and its low-level center will likely become disorganized over the high terrain. However, the strong burst of convection currently near Puerto Rico is associated with a mid-level circulation, which should pass along the north coast of Hispaniola later today. Most of the model guidance suggest that this feature will cause the re-development of a surface center over the northern part of the broader system while the mid-level circulation moves close to the southeastern Bahamas. Afterward, the cyclone would then move northwestward until the weekend, and gradually turn northward and northeastward close to the U.S. East Coast into early next week ahead of a mid-latitude trough. The official track forecast is a little to the east of the previous one and close to the NOAA corrected dynamical model consensus. It should be noted that further adjustments to the forecast tracks are indeed possible, especially after Isaias moves north of Hispaniola. The intensity forecast is quite tricky. In the short term, Isaias is expected to move across Hispaniola, as the storm's interaction with the mountainous island should cause some weakening and disruption to the circulation. However, as mentioned before, the models suggest that a new center could form, and the environmental conditions would support gradual intensification. The intensity models have been trending higher, and the official forecast is nudged upward accordingly, now showing a peak intensity of 60 kt when the storm is near the coast of Florida and the Southeast U.S. Coast. It should be noted that there are models that show hurricane strength near the U.S. but, given the large amount of uncertainty, it is preferred to stay on the conservative side for now. We should have a better idea of how strong Isaias will become near the U.S. after reconnaissance aircraft sample the storm and after it passes Hispaniola later today.

al092020 Tropical Storm Isaias