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Tropical Storm Isaias Forecast Discussion Number 9

2020-07-30 16:51:21| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Jul 30 2020 000 WTNT44 KNHC 301451 TCDAT4 Tropical Storm Isaias Discussion Number 9 NWS National Hurricane Center Miami FL AL092020 1100 AM AST Thu Jul 30 2020 The satellite presentation of Isaias has improved over the past 24 hours with a concentrated area of deep convection occurring near and to the northeast of the low-level center. Radar imagery from Puerto Rico has shown a mid-level circulation that moved over the Mona passage and is now along the northern coast of Hispaniola. Surface observations and data from an Air Force Reserve reconnaissance aircraft, however, continue to place the center near the southeastern coast of Hispaniola. It is possible that a new center will re-form along the northern coast of Hispaniola as the system interacts with high terrain of that island later today or tonight. The initial intensity remains 50 kt, and is based on the earlier Doppler radar data and observations along the southern coast of Puerto Rico. Isaias is moving northwestward or 310/16 kt. A high pressure ridge over the western Atlantic should steer Isaias on a west- northwestward to northwestward heading over the next couple of days, but the likelihood of a center re-formation during the next 12-18 hours means that some adjustments to the track and motion are possible. By late Friday, a mid-latitude trough moving into the east-central United States is expected to weaken the western portion of the ridge. This pattern should cause the cyclone to turn northwestward to north-northwestward on Saturday when it is near the northwestern Bahamas and South Florida. As the trough slides eastward over the United States, this should steer Isaias northward and northeastward early next week. Although the bulk of the track guidance agrees on this overall scenario, the confidence in the track forecast remains lower than usual due to the expected land interaction and possible center reformation in the short term. The new NHC track forecast is a blend of the HFIP corrected consensus and the TCVA multi-model consensus, and is similar to the previous advisory. The intensity forecast remains challenging. The structure of the storm is likely to be disrupted by its passage near or over Hispaniola today, and some weakening is likely. Once the system moves away from the Greater Antilles gradual strengthening is anticipated. The global models and the SHIPS guidance suggest that Isaias will encounter an area of moderate southwesterly shear over the weekend, and the NHC intensity forecast is again leveled off at that time. There are models that continue to suggest Isaias could become a hurricane when it is near the U.S., but given the continued uncertainty, the NHC intensity forecast remains near the intensity consensus. Key Messages: 1. Isaias will produce heavy rains and potentially life-threatening flash flooding and mudslides across Puerto Rico, the Dominican Republic, northern Haiti, the Turks and Caicos, and the Bahamas. Heavy rains associated with Isaias may begin to affect South Florida Saturday morning, potentially resulting in isolated flash and urban flooding. 2. Tropical storm conditions will continue across portions of the Virgin Islands and Puerto Rico through early afternoon and will spread across portions of the Dominican Republic, Haiti, the Turks and Caicos and the Bahamas later today through Friday, and 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. There is a risk of impacts from winds, heavy rainfall, and storm surge along portions of the U.S. east coast beginning this weekend in Florida and spreading northward to the Carolinas and southern mid-Atlantic states early next week. Due to Isaias interacting with Hispaniola, the details of the track and intensity forecast remain uncertain and it is too soon to determine the magnitude and location of these potential impacts. Interests in these areas should monitor the progress of Isaias and updates to the forecast. Tropical storm or hurricane watches could be issued for portions of South Florida later today. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 18.1N 68.9W 50 KT 60 MPH 12H 31/0000Z 19.7N 71.4W 45 KT 50 MPH...INLAND 24H 31/1200Z 21.4N 74.2W 50 KT 60 MPH...OVER WATER 36H 01/0000Z 23.0N 76.5W 55 KT 65 MPH 48H 01/1200Z 24.6N 78.2W 60 KT 70 MPH 60H 02/0000Z 26.2N 79.4W 60 KT 70 MPH 72H 02/1200Z 28.0N 79.9W 60 KT 70 MPH 96H 03/1200Z 31.5N 79.1W 60 KT 70 MPH 120H 04/1200Z 37.5N 73.5W 60 KT 70 MPH $$ Forecaster Brown

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Tropical Storm Isaias Forecast Advisory Number 9

2020-07-30 16:50:20| National Hurricane Center (Atlantic)

Issued at 1500 UTC THU JUL 30 2020 000 WTNT24 KNHC 301450 TCMAT4 TROPICAL STORM ISAIAS FORECAST/ADVISORY NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092020 1500 UTC THU JUL 30 2020 CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY... THE GOVERNMENT OF ANTIGUA HAS DISCONTINUED THE TROPICAL STORM WARNING FOR THE BRITISH VIRGIN ISLANDS. SUMMARY OF WATCHES AND WARNINGS IN EFFECT... A TROPICAL STORM WARNING IS IN EFFECT FOR... * PUERTO RICO...VIEQUES...CULEBRA * U.S. 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. WATCHES MAY BE REQUIRED FOR A PORTION OF THE FLORIDA PENINSULA LATER TODAY. 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. TROPICAL STORM CENTER LOCATED NEAR 18.1N 68.9W AT 30/1500Z POSITION ACCURATE WITHIN 75 NM PRESENT MOVEMENT TOWARD THE NORTHWEST OR 310 DEGREES AT 17 KT ESTIMATED MINIMUM CENTRAL PRESSURE 1003 MB MAX SUSTAINED WINDS 50 KT WITH GUSTS TO 60 KT. 50 KT....... 80NE 0SE 0SW 0NW. 34 KT.......270NE 90SE 0SW 210NW. 12 FT SEAS..420NE 0SE 0SW 360NW. WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT. REPEAT...CENTER LOCATED NEAR 18.1N 68.9W AT 30/1500Z AT 30/1200Z CENTER WAS LOCATED NEAR 17.7N 68.5W FORECAST VALID 31/0000Z 19.7N 71.4W...INLAND MAX WIND 45 KT...GUSTS 55 KT. 34 KT...210NE 90SE 0SW 160NW. FORECAST VALID 31/1200Z 21.4N 74.2W...OVER WATER MAX WIND 50 KT...GUSTS 60 KT. 50 KT... 40NE 0SE 0SW 0NW. 34 KT...180NE 90SE 0SW 150NW. FORECAST VALID 01/0000Z 23.0N 76.5W MAX WIND 55 KT...GUSTS 65 KT. 50 KT... 40NE 20SE 0SW 0NW. 34 KT...140NE 90SE 30SW 90NW. FORECAST VALID 01/1200Z 24.6N 78.2W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 40NE 20SE 0SW 20NW. 34 KT...120NE 90SE 50SW 90NW. FORECAST VALID 02/0000Z 26.2N 79.4W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 40NE 30SE 20SW 20NW. 34 KT...120NE 90SE 50SW 70NW. FORECAST VALID 02/1200Z 28.0N 79.9W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 40NE 30SE 20SW 20NW. 34 KT...120NE 90SE 50SW 60NW. EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 150 NM ON DAY 4 AND 175 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY OUTLOOK VALID 03/1200Z 31.5N 79.1W MAX WIND 60 KT...GUSTS 75 KT. OUTLOOK VALID 04/1200Z 37.5N 73.5W MAX WIND 60 KT...GUSTS 75 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 18.1N 68.9W INTERMEDIATE PUBLIC ADVISORY...WTNT34 KNHC/MIATCPAT4...AT 30/1800Z NEXT ADVISORY AT 30/2100Z $$ FORECASTER BROWN

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Tropical Storm Isaias Forecast Discussion Number 8

2020-07-30 10:52:45| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Jul 30 2020 000 WTNT44 KNHC 300852 TCDAT4 Tropical Storm Isaias Discussion Number 8 NWS National Hurricane Center Miami FL AL092020 500 AM AST Thu Jul 30 2020 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. Key Messages: 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. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 17.2N 67.9W 50 KT 60 MPH 12H 30/1800Z 18.8N 70.2W 45 KT 50 MPH...INLAND 24H 31/0600Z 20.6N 72.9W 45 KT 50 MPH...OVER WATER 36H 31/1800Z 22.3N 75.5W 50 KT 60 MPH 48H 01/0600Z 24.0N 77.9W 55 KT 65 MPH 60H 01/1800Z 25.5N 79.2W 60 KT 70 MPH 72H 02/0600Z 27.3N 80.0W 60 KT 70 MPH 96H 03/0600Z 31.0N 80.0W 60 KT 70 MPH 120H 04/0600Z 37.0N 74.5W 60 KT 70 MPH $$ Forecaster Blake/Cangialosi

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Tropical Storm Isaias Forecast Advisory Number 8

2020-07-30 10:46:44| National Hurricane Center (Atlantic)

Issued at 0900 UTC THU JUL 30 2020 000 WTNT24 KNHC 300846 TCMAT4 TROPICAL STORM ISAIAS FORECAST/ADVISORY NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092020 0900 UTC THU JUL 30 2020 CHANGES IN WATCHES AND WARNINGS 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. TROPICAL STORM CENTER LOCATED NEAR 17.2N 67.9W AT 30/0900Z POSITION ACCURATE WITHIN 75 NM PRESENT MOVEMENT TOWARD THE NORTHWEST OR 305 DEGREES AT 18 KT ESTIMATED MINIMUM CENTRAL PRESSURE 1003 MB MAX SUSTAINED WINDS 50 KT WITH GUSTS TO 60 KT. 50 KT....... 90NE 0SE 0SW 0NW. 34 KT.......360NE 60SE 0SW 240NW. 12 FT SEAS..420NE 0SE 0SW 300NW. WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT. REPEAT...CENTER LOCATED NEAR 17.2N 67.9W AT 30/0900Z AT 30/0600Z CENTER WAS LOCATED NEAR 16.7N 67.2W FORECAST VALID 30/1800Z 18.8N 70.2W...INLAND MAX WIND 45 KT...GUSTS 55 KT. 34 KT...240NE 90SE 0SW 180NW. FORECAST VALID 31/0600Z 20.6N 72.9W...OVER WATER MAX WIND 45 KT...GUSTS 55 KT. 34 KT...180NE 90SE 0SW 150NW. FORECAST VALID 31/1800Z 22.3N 75.5W MAX WIND 50 KT...GUSTS 60 KT. 50 KT... 40NE 0SE 0SW 0NW. 34 KT...140NE 90SE 30SW 100NW. FORECAST VALID 01/0600Z 24.0N 77.9W MAX WIND 55 KT...GUSTS 65 KT. 50 KT... 40NE 20SE 0SW 20NW. 34 KT...120NE 90SE 50SW 90NW. FORECAST VALID 01/1800Z 25.5N 79.2W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 40NE 30SE 20SW 20NW. 34 KT...120NE 90SE 50SW 70NW. FORECAST VALID 02/0600Z 27.3N 80.0W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 40NE 30SE 20SW 20NW. 34 KT...120NE 90SE 50SW 70NW. EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 150 NM ON DAY 4 AND 175 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY OUTLOOK VALID 03/0600Z 31.0N 80.0W MAX WIND 60 KT...GUSTS 75 KT. OUTLOOK VALID 04/0600Z 37.0N 74.5W MAX WIND 60 KT...GUSTS 75 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 17.2N 67.9W INTERMEDIATE PUBLIC ADVISORY...WTNT34 KNHC/MIATCPAT4...AT 30/1200Z NEXT ADVISORY AT 30/1500Z $$ FORECASTER BLAKE

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Tropical Storm Isaias Forecast Discussion Number 7

2020-07-30 05:01:12| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Jul 29 2020 991 WTNT44 KNHC 300301 TCDAT4 Tropical Storm Isaias Discussion Number 7 NWS National Hurricane Center Miami FL AL092020 1100 PM AST Wed Jul 29 2020 Observations from recent scatterometer passes over the system show that it now has a sufficiently well-defined center to be designated as a tropical cyclone. The current intensity is estimated to be 45 kt, but these winds are currently occurring over the Atlantic waters well to the north and northeast of the center. Since the cyclone is expected to move over Hispaniola on Thursday some weakening is likely within the next 24 hours. However since Isaias has such a broad wind field, the weakening will probably not be as significant as in a typical tropical cyclone with a small radius of maximum winds. Also, a re-formation of the center to the north of Hispaniola may occur. Later in the forecast period some strengthening is likely, although this may be offset by southwesterly wind shear on the order of 20 kt in 2-3 days. The official forecast is close to the intensity model consensus but well below the latest LGEM guidance. The scatterometer data show that the center of the system is south of the previously estimated track, so there is a lot of uncertainty in the initial motion estimate of 285/17 kt. Isaias should move on a west-northwestward to northwestward track on the southern and southwestern side of a mid-tropospheric ridge. In 2-3 days, the system is expected to turn north-northwestward due to a weakness in the ridge and an approaching trough. Later in the forecast period, the trough should cause Isaias to turn toward the northeast. The official track forecast is a little to the east of the previous one and a little west of the simple and corrected dynamical model consensus tracks. It should be noted that further adjustments to the forecast tracks are indeed possible, especially after Isaias moves north of Hispaniola. Key Messages: 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 southeastern Bahamas. 2. Tropical storm conditions are likely across portions of the 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 and the Central Bahamas on Thursday 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, the northwestern 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. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 15.8N 67.0W 45 KT 50 MPH 12H 30/1200Z 17.6N 69.3W 45 KT 50 MPH 24H 31/0000Z 19.4N 72.2W 40 KT 45 MPH...INLAND 36H 31/1200Z 21.4N 74.8W 45 KT 50 MPH...OVER WATER 48H 01/0000Z 22.9N 77.3W 50 KT 60 MPH 60H 01/1200Z 24.8N 79.2W 55 KT 65 MPH 72H 02/0000Z 26.6N 80.2W 55 KT 65 MPH...INLAND 96H 03/0000Z 30.0N 80.5W 55 KT 65 MPH...INLAND 120H 04/0000Z 35.0N 77.0W 50 KT 60 MPH...INLAND $$ Forecaster Pasch

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