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Tropical Storm Henri Forecast Discussion Number 20

2021-08-20 22:42:48| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Fri Aug 20 2021 000 WTNT43 KNHC 202042 TCDAT3 Tropical Storm Henri Discussion Number 20 NWS National Hurricane Center Miami FL AL082021 500 PM EDT Fri Aug 20 2021 Henri appears to be slowly gaining strength. Deep convection has been increasing during the past few hours and the upper-level outflow continues to become better established on the east side of the circulation. However, the low-level center is still located near the northwestern edge of the deep convection due to ongoing northerly wind shear. An ASCAT-B pass from a few hours ago showed peak winds of around 55 kt, with the strongest winds on the southeast side of the circulation. Based on this data, the initial intensity is set at 60 kt. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate Henri again this evening and the data the plane collects will be very helpful in estimating the storm's strength and structure. The tropical storm appears to be making the advertised turn to the right, with the latest initial motion estimated to be 335/6 kt. A trough over the central Appalachians is expected to cut off tonight, and the combination of that feature and a building ridge to the east/northeast of Henri should cause the storm to accelerate to the north on Saturday. The latest model runs have generally trended to the left again and are a bit faster, with most showing landfall in about 48 hours. Most of the models now show a slight left turn before landfall as Henri gets caught in the circulation of the aforementioned trough. The latest GFS and ECMWF ensemble members continue to span a region from near New York City to Cape Cod for the landfall point. Based on the latest consensus aids, the official track forecast has again been nudged to the west of the previous one and shows landfall occurring on Sunday. After day 3, Henri is forecast to eject northeastward. The ongoing northerly shear is expected to decrease tonight, and the global models show a favorable upper-level wind pattern developing over the storm through the weekend. These more conducive atmospheric conditions combined with the warm Gulf Stream waters should allow Henri to strengthen to a hurricane tonight or early Saturday, with additional intensification expected into Saturday night. By early Sunday, however, Henri is forecast to cross the north wall of the Gulf Stream, and that should end its opportunity for strengthening. Although steady to rapid weakening is forecast while Henri moves over cooler waters south of Long Island and New England, it will likely still be at or very near hurricane intensity when it reaches the coast. Post-tropical transition is forecast to occur by day 3 and the system should dissipate in 4 or 5 days. Users are reminded to not focus on the exact forecast of the center of Henri since impacts will extend far from the center. Key Messages: 1. Dangerous storm surge inundation is expected to begin Sunday in portions of Long Island, Connecticut, Rhode Island, and southeastern Massachusetts, where a Storm Surge Warning has been issued. Dangerous storm surge is possible beginning Sunday in western portions of Long Island and Connecticut in the Storm Surge Watch area. Residents in these areas should follow any advice given by local officials. 2. Hurricane conditions are expected to begin Sunday in portions of Long Island and Connecticut, where a Hurricane Warning has been issued. Hurricane conditions are possible Sunday across portions of Rhode Island and southeastern Massachusetts. 3. Heavy rainfall may lead to considerable flash, urban, and small stream flooding, along with the potential for widespread minor and isolated moderate river flooding, over portions of Long Island and New England Sunday into Monday. 4. Swells from Henri will continue to affect much of the east coast of the U.S. through the weekend. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 31.2N 73.9W 60 KT 70 MPH 12H 21/0600Z 32.8N 73.3W 65 KT 75 MPH 24H 21/1800Z 35.8N 72.3W 75 KT 85 MPH 36H 22/0600Z 38.9N 71.9W 75 KT 85 MPH 48H 22/1800Z 40.8N 72.4W 65 KT 75 MPH 60H 23/0600Z 42.0N 72.8W 45 KT 50 MPH...INLAND 72H 23/1800Z 42.9N 72.6W 30 KT 35 MPH...POST-TROPICAL 96H 24/1800Z 43.8N 68.9W 25 KT 30 MPH...POST-TROPICAL 120H 25/1800Z...DISSIPATED $$ Forecaster Cangialosi

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Hurricane Grace Forecast Discussion Number 29

2021-08-20 16:48:07| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Fri Aug 20 2021 000 WTNT42 KNHC 201448 TCDAT2 Hurricane Grace Discussion Number 29 NWS National Hurricane Center Miami FL AL072021 1000 AM CDT Fri Aug 20 2021 Grace is a strengthening tropical cyclone. Its structure has continued to improve in satellite imagery this morning, with more pronounced curved banding in its northern and eastern semicircles and good upper-level outflow. An Air Force Reserve Hurricane Hunter aircraft measured a peak 850-mb flight-level wind of 92 kt and peak SFMR winds of 74 kt during a pass through the northeast quadrant earlier this morning. These data support increasing the initial intensity of 75 kt, which makes Grace a hurricane once again. Dropsonde data from the aircraft indicate the minimum pressure has fallen to 982 mb. The warm waters of the Bay of Campeche are expected to support additional intensification through landfall in mainland Mexico later this evening or tonight, despite some light to moderate northerly wind shear. Since the reconnaissance data revealed Grace is strengthening quicker than previously forecast, the official NHC intensity forecast was increased in the short-term. Grace is now forecast to become a 90-kt hurricane in 12 h, which lies on the high end of the intensity guidance. The center of Grace will be well inland by 24 h, and rapid weakening is forecast thereafter as the cyclone moves over the mountains of central Mexico. Although Grace is forecast to dissipate by 48 h, its remnants will likely move into the eastern Pacific and lead to the development of a new tropical cyclone later this weekend or early next week. The cyclone is moving just south of due west, or 265/12 kt. Grace should continue moving westward to west-southwestward through landfall to the south of a mid-level ridge over the northern Gulf of Mexico. The official NHC track forecast remains near the middle of the guidance envelope and has been adjusted just a bit southward based on the latest multi-model consensus aids. Key Messages: 1. Hurricane conditions and dangerous storm surge are likely along portions of eastern mainland Mexico beginning late today within the Hurricane Warning area from Puerto Veracruz northward to Cabo Rojo. 2. Through the weekend, heavy rainfall across Veracruz, Puebla, Tlaxcala, Hidalgo, northern Queretaro, and eastern San Luis Potosi will lead to flash and urban flooding, along with the likelihood of mudslides. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 20.6N 94.3W 75 KT 85 MPH 12H 21/0000Z 20.4N 95.9W 90 KT 105 MPH 24H 21/1200Z 20.0N 98.2W 55 KT 65 MPH...INLAND 36H 22/0000Z 19.4N 101.1W 35 KT 40 MPH...INLAND 48H 22/1200Z...DISSIPATED $$ Forecaster Reinhart/Cangialosi

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Tropical Storm Henri Forecast Discussion Number 19

2021-08-20 16:45:38| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Fri Aug 20 2021 000 WTNT43 KNHC 201445 TCDAT3 Tropical Storm Henri Discussion Number 19 NWS National Hurricane Center Miami FL AL082021 1100 AM EDT Fri Aug 20 2021 The Air Force Reserve Hurricane Hunters investigated Henri this morning and based on the flight-level, SFMR, and dropsonde data, the initial intensity is still around 55 kt. The minimum pressure has also been relatively steady. The low-level center of Henri is located close to the northwestern edge of the main area of deep convection, and the vortex is still not vertically aligned due to 20-25 kt of northerly vertical wind shear. Although the intensity of Henri has not changed much during the past couple of days, satellite images show an improving cloud pattern with well- established outflow in the eastern semicircle, which could indicate that Henri is poised to strengthen. There is some uncertainty in the exact position of Henri given the recent aircraft fixes and the tilt of the vortex, but the initial motion appears to be northwestward at 6 kt. A trough over the central Appalachians is expected to cut off tonight, and the combination of that feature and a building ridge to the east/northeast of Henri should cause the storm to turn northward tonight and accelerate in that direction on Saturday. Some of the models show a slight bend to the west around the time Henri is forecast to make landfall on Sunday, and there remains a fair amount spread in the guidance in where the center of Henri will come ashore. The latest GFS and ECMWF ensemble members span a region from near New York City to Cape Cod for the landfall point. Based on the latest consensus aids and initial position, the official track forecast is nudged to the west of the previous one and shows landfall occurring by late Sunday. After day 3, Henri is forecast to eject northeastward across the Gulf of Maine. The ongoing northerly shear is expected to decrease later today, and the global models show a favorable upper-level wind pattern developing over the storm later today through the weekend. These more conducive atmospheric conditions combined with the warm Gulf Stream waters should allow Henri to strengthen to a hurricane tonight or early Saturday with additional intensification expected into Saturday night. By early Sunday, however, Henri is forecast to cross the north wall of the Gulf Stream, and that should end its opportunity for strengthening. Although steady to rapid weakening is forecast while Henri moves over cooler waters south of New England, it will likely still be at or very near hurricane intensity when it reaches the coast. Post-tropical transition is forecast to occur in 3 to 4 days, and the new forecast shows Henri dissipated by day 5, in agreement with most of the global models. Users are reminded to not focus on the exact forecast of the center of Henri since impacts will extend far from the center. Key Messages: 1. Dangerous storm surge inundation and hurricane conditions are possible beginning Sunday in portions of Long Island, Connecticut, Rhode Island, and southeastern Massachusetts, where a Storm Surge Watch and Hurricane Watch are in effect. Residents in these areas should follow any advice given by local officials. 2. Heavy rainfall may lead to flash, urban, and small stream flooding, along with the potential for widespread minor and isolated moderate river flooding, over portions of southern New England Sunday into Monday. 3. Swells from Henri will begin to reach much of the east coast of the U.S. and Atlantic Canada by the end of the week and continue through the weekend. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 30.4N 73.7W 55 KT 65 MPH 12H 21/0000Z 31.5N 73.7W 60 KT 70 MPH 24H 21/1200Z 34.1N 72.7W 70 KT 80 MPH 36H 22/0000Z 37.3N 71.8W 75 KT 85 MPH 48H 22/1200Z 39.8N 71.7W 65 KT 75 MPH 60H 23/0000Z 41.4N 71.8W 60 KT 70 MPH...INLAND 72H 23/1200Z 42.4N 71.8W 40 KT 45 MPH...INLAND 96H 24/1200Z 43.7N 69.4W 35 KT 40 MPH...POST-TROPICAL 120H 25/1200Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Storm Henri Forecast Discussion Number 18

2021-08-20 10:59:34| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Fri Aug 20 2021 000 WTNT43 KNHC 200859 TCDAT3 Tropical Storm Henri Discussion Number 18 NWS National Hurricane Center Miami FL AL082021 500 AM EDT Fri Aug 20 2021 Henri's low-level center has been peaking out from under the north side of the deep convective mass, resulting from continued 20-25 kt of northerly shear. Maximum winds are still estimated to be 55 kt based on T3.5 Dvorak estimates from TAFB and SAB. Henri still has a motion toward the west-northwest, or 300/8 kt, but it is about ready to make the sharp right turn that we've been expecting. A shortwave trough currently over the central Appalachians is forecast to close off by Saturday, with Henri accelerating northward on the east side of this feature through the weekend. Some global models show Henri merging with the mid-/upper-level low as the cyclone approaches southern New England, which induces a slight bend of Henri's forecast track to the left. Nearly all track models now show Henri's center reaching the coast of southern New England, and the new NHC track forecast has been nudged westward in the direction of HCCA and the other consensus aids. After day 3, Henri is forecast to eject northeastward across the Gulf of Maine toward Atlantic Canada. The strong shear affecting Henri is forecast to begin weakening later today, and SHIPS diagnostics indicate that it could drop to less than 10 kt in about 36 hours. In addition, Henri will be traversing very warm waters for the next 48 hours before it crosses the north wall of the Gulf Stream. Therefore, strengthening is anticipated for the next 2 days, with Henri likely to become a hurricane by Saturday. After 48 hours, Henri's expected slower motion over the colder water south of New England should induce quick weakening, but it may not be quick enough to keep Henri from reaching the coast as a hurricane. Faster weakening is anticipated after Henri's center moves over land, and simulated satellite imagery from the GFS and ECMWF models suggest that deep convection could dissipate by day 4, making Henri a post-tropical low at that time. Global models suggest that Henri may dissipate by day 5, but for the time being a day 5 point is being kept for continuity. Based on the new forecast, tropical-storm-force wind radii will be approaching the coast of southern New England in about 48 hours. Given the still-present uncertainties in Henri's future track and intensity and the hazards that the storm may cause, storm surge and hurricane watches are now being issued for portions of Long Island, Connecticut, Rhode Island, and southeastern Massachusetts. Users are reminded to not focus on the exact forecast points as impacts will extend far from the center. Key Messages: 1. Henri is forecast to be near the northeast coast of the U.S. on Sunday and Monday, and the risks of storm surge, wind, and rain impacts in portions of southern New England and eastern Long Island are increasing. Hurricane and storm surge watches are now in effect for portions of Long Island, Connecticut, Rhode Island, and southeastern Massachusetts. Additional watches or warnings may be required later today. 2. Swells from Henri will begin to reach much of the east coast of the U.S. and Atlantic Canada by the end of the week and continue through the weekend. These swells could cause life-threatening surf and rip currents. 3. Heavy rainfall may lead to flash, urban, and small stream flooding over portions of southern New England Sunday into Monday. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 30.2N 73.1W 55 KT 65 MPH 12H 20/1800Z 31.0N 73.5W 55 KT 65 MPH 24H 21/0600Z 33.0N 72.9W 60 KT 70 MPH 36H 21/1800Z 36.1N 71.8W 70 KT 80 MPH 48H 22/0600Z 39.1N 71.1W 75 KT 85 MPH 60H 22/1800Z 41.1N 71.3W 65 KT 75 MPH 72H 23/0600Z 42.2N 71.6W 50 KT 60 MPH...INLAND 96H 24/0600Z 43.5N 70.0W 35 KT 40 MPH...POST-TROPICAL 120H 25/0600Z 45.3N 63.0W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg

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Tropical Storm Grace Forecast Discussion Number 28

2021-08-20 10:52:38| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Fri Aug 20 2021 000 WTNT42 KNHC 200852 TCDAT2 Tropical Storm Grace Discussion Number 28 NWS National Hurricane Center Miami FL AL072021 400 AM CDT Fri Aug 20 2021 Deep convection has increased near the center of Grace overnight with improved banding structure over the eastern portion of the circulation. An Air Force Reserve Hurricane Hunter aircraft measured a peak 850-mb flight-level wind of 72 kt and SFMR winds of 58 kt during the aircraft's final pass through the northern portion of the storm prior to 06Z. Based on those observations, the initial wind speed was increased to 60 kt on the 06Z intermediate advisory, and it remains at that value for now. Grace is close to re-gaining hurricane strength, and the next reconnaissance mission should be in the storm around 1200 UTC this morning. Grace will be moving over the warm waters over the Bay of Campeche today. That, along with light to moderate vertical wind shear conditions, are expected to allow for re-intensification until landfall in mainland Mexico tonight. The updated intensity forecast brings Grace to a 75-kt hurricane in 12 hours, and the storm could be slightly stronger when it makes landfall overnight. By 24 h, the center is forecast to be inland, and Grace will likely already to have begun to weaken. Rapid weakening should occur on Saturday as Grace moves farther inland over the mountainous terrain of central Mexico, and the circulation is likely to dissipate in around 48 hours. The remnants of Grace are expected to move into the Pacific where they are likely to spawn a new tropical cyclone. The cyclone has been moving westward or 270/14 kt. A strong mid-level ridge to the north of Grace should continue to steer the cyclone westward to west-southwestward until dissipation occurs in a couple days. The new NHC track forecast is near the middle of the guidance envelope and is essentially unchanged from the previous advisory. Key Messages: 1. Hurricane conditions and dangerous storm surge are likely along portions of eastern mainland Mexico beginning late today. A Hurricane Warning is in effect from Puerto Veracruz northward to Cabo Rojo. 2. Through the weekend, heavy rainfall across Veracruz, Puebla, Tlaxcala, Hidalgo, northern Queretaro, and eastern San Luis Potosi will lead to flash and urban flooding, along with the likelihood of mudslides. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 20.7N 93.3W 60 KT 70 MPH 12H 20/1800Z 20.6N 95.2W 75 KT 85 MPH 24H 21/0600Z 20.3N 97.4W 70 KT 80 MPH...INLAND 36H 21/1800Z 19.8N 99.7W 35 KT 40 MPH...INLAND 48H 22/0600Z 19.4N 102.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 22/1800Z...DISSIPATED $$ Forecaster Brown

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