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Tropical Storm Marty Forecast Discussion Number 1

2021-08-23 10:37:13| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Mon Aug 23 2021 000 WTPZ43 KNHC 230837 TCDEP3 Tropical Storm Marty Discussion Number 1 NWS National Hurricane Center Miami FL EP132021 300 AM MDT Mon Aug 23 2021 Recent scatterometer wind data indicate that the circulation associated with the low pressure area located a couple of hundred miles south-southwest of the southern tip of the Baja California peninsula has become better defined. In addition, convective activity has persisted and expanded over the western portion of the circulation overnight, resulting in Dvorak T-numbers of 1.5 and 2.0 from SAB and TAFB, respectively. Both ASCAT-A and B instruments revealed 30 to 35 kt winds over the western portion of the circulation and based on these data, advisories are being initiated on Tropical Storm Marty, the thirteenth named-storm of the 2021 eastern Pacific hurricane season. Marty is moving westward at about 13 kt. A strong mid-tropospheric ridge that extends from the south-central United States westward across northern Mexico and the eastern Pacific is forecast to steer Marty westward over the next couple of days. After that time, the cyclone is forecast to weaken and become vertically shallow. This should cause it to turn toward the west-southwest as it steered by the low-level trade wind flow. The dynamical model guidance is in excellent agreement, and the NHC track is near the middle of the tightly clustered model envelope. Although the tropical storm is currently located over warm waters, it is within an area of moderate northeasterly shear. In addition, it is likely to ingest drier and more stable air located to the northwest of the system over the next couple of days. As a result, only slight strengthening is indicated in the official forecast. By 36 hours, Marty is forecast to cross the 26C isotherm and gradual weakening is anticipated after that time. Less favorable thermodynamic conditions should result in the system becoming a remnant low in 60 to 72 hours, if not sooner. The NHC intensity forecast is in good agreement with the HCCA and IVCN consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 20.0N 111.0W 35 KT 40 MPH 12H 23/1800Z 20.3N 113.2W 40 KT 45 MPH 24H 24/0600Z 20.4N 116.0W 40 KT 45 MPH 36H 24/1800Z 20.2N 118.4W 35 KT 40 MPH 48H 25/0600Z 20.1N 120.4W 30 KT 35 MPH 60H 25/1800Z 20.0N 122.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 26/0600Z 19.8N 124.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 27/0600Z 19.0N 129.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 28/0600Z...DISSIPATED $$ Forecaster Brown

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Tropical Depression Henri Forecast Discussion Number 29

2021-08-23 04:44:07| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sun Aug 22 2021 000 WTNT43 KNHC 230243 TCDAT3 Tropical Depression Henri Discussion Number 29 NWS National Hurricane Center Miami FL AL082021 1100 PM EDT Sun Aug 22 2021 Henri has continued to weaken over land and synoptic surface observations indicate that its maximum winds have decreased to near 25 kt. A little more weakening is likely during the next 48 hours, and simulated satellite imagery from the global models indicate that the system will be post-tropical after its expected re-emergence into the Atlantic in 36 hours or so. Beyond 48 hours the dynamical guidance suggests that the system will lose its identity. Satellite imagery and surface data indicate that the center is moving slowly west-northwestward, or 290/7 kt. Henri is interacting with another cyclonic circulation over the northeastern United States. As a result of this interaction, the tropical cyclone is expected to briefly come to a halt overnight, turn toward the east-northeast on Monday, and continue an east-northeastward motion into Tuesday. The official forecast track is similar to the dynamical model consensus, TVCN. Although Henri's winds are weakening, the cyclone will still continue to be a prolific rain producer, resulting in significant flooding across southern New England and portions of the northern mid-Atlantic states for the next day or two. This is the last advisory by the National Hurricane Center on Henri. Future information on this system can be found in Public Advisories issued by the Weather Prediction Center beginning at 5 AM EDT, under AWIPS header TCPAT3, WMO header WTNT33 KWNH, and on the web at http://www.wpc.ncep.noaa.gov. Key Messages: 1. Heavy rainfall will continue to lead to considerable flash, urban, and small stream flooding, along with the potential for additional minor to isolated moderate river flooding over portions of Long Island, New England, eastern New York, New Jersey and northeast Pennsylvania. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 41.9N 73.2W 25 KT 30 MPH...INLAND 12H 23/1200Z 42.1N 73.6W 25 KT 30 MPH...INLAND 24H 24/0000Z 42.4N 72.5W 25 KT 30 MPH...INLAND 36H 24/1200Z 42.8N 69.5W 25 KT 30 MPH...POST-TROPICAL 48H 25/0000Z 43.4N 65.5W 20 KT 25 MPH...POST-TROPICAL 60H 25/1200Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Henri Forecast Discussion Number 28

2021-08-22 22:53:32| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Sun Aug 22 2021 000 WTNT43 KNHC 222053 TCDAT3 Tropical Storm Henri Discussion Number 28 NWS National Hurricane Center Miami FL AL082021 500 PM EDT Sun Aug 22 2021 Henri's satellite and radar signatures have continued to erode during the day today owing to moderate southeasterly vertical wind shear and entrainment of drier and more stable air off of the cooler Atlantic waters. The primary rain shield has shifted into the western semicircle, which is typical for tropical cyclones that are in the early stages of undergoing extratropical transition. Doppler radar velocity data from Upton, New York, and Boston, Massachusetts, along with surface observations indicate that Henri's peak winds have continued to decrease, with any tropical-storm-force winds now confined to the offshore waters of Long Island Sound. Additional spin down of the vortex and weakening of the low-level wind field are anticipated due to land interaction and entrainment of additional stable air. As a result of these unfavorable conditions, Henri should weaken to a tropical depression this evening, and become a post-tropical remnant low by Monday afternoon or evening. Henri is now moving west-northwestward or 290/06 kt. The tropical storm has finally made the much anticipated sharp turn toward the west-northwest around the northeastern periphery of a mid- to upper-level low currently located over southern New Jersey. These two weather systems are forecast to slowly dumbbell in a counter- clockwise motion, with Henri's circulation absorbing the other low by Monday morning, possibly resulting in Henri stalling near the New York-Connecticut border. By early Monday afternoon, a weak mid-tropospheric shortwave currently moving across the Great Lakes region is expected to eject the cyclone or its remnants eastward to east-northeastward across southern New England and into the Gulf of Maine by Monday night, before dissipating near or over Nova Scotia on Tuesday. The new NHC track forecast is similar to the previous advisory track, and remains close to the tightly packed simple- and corrected-consensus track models TVCA, HCCA, and FSSE. Although Henri's winds will be weakening, the cyclone will still continue to be a prolific rain producer, resulting in significant flooding across southern New England and portions of the northern mid-Atlantic states for the next day or two. Key Messages: 1. Heavy rainfall will continue to lead to considerable flash, urban, and small stream flooding, along with the potential for additional minor to isolated moderate river flooding over portions of Long Island, New England, eastern New York, New Jersey and northeast Pennsylvania. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 41.6N 72.4W 35 KT 40 MPH...INLAND 12H 23/0600Z 42.0N 73.5W 30 KT 35 MPH...INLAND 24H 23/1800Z 42.6N 73.0W 25 KT 30 MPH...INLAND 36H 24/0600Z 43.0N 70.4W 25 KT 30 MPH...POST-TROP/INLAND 48H 24/1800Z 43.6N 66.5W 25 KT 30 MPH...POST-TROP/INLAND 60H 25/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Henri Forecast Discussion Number 27

2021-08-22 17:01:27| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sun Aug 22 2021 000 WTNT43 KNHC 221501 TCDAT3 Tropical Storm Henri Discussion Number 27 NWS National Hurricane Center Miami FL AL082021 1100 AM EDT Sun Aug 22 2021 Henri's presentation in both satellite and radar imagery has degraded significantly since the previous advisory due to the cyclone having moved over much cooler water. An eyewall feature is no longer evident and clouds tops have warmed markedly in the inner-core region around the center. Data from an Air Force Reserve reconnaissance aircraft, NOAA Doppler weather radars, and surface observations indicate that Henri's peak winds have decreased to 50 kt despite the central pressure remaining constant at about 987 mb. Henri is moving north-northwestward or 335/10 kt. The cyclone is forecast to gradually turn northwestward later this afternoon and possibly even move westward before stalling near the New York-Connecticut border later tonight owing to interaction with a mid- to upper-level low located over he DelMarVa region. The latter system is expected to be absorbed by Henri by early Monday morning before ejecting out slowly eastward to east-northeastward across southern New England by Monday afternoon and evening. Henri is then forecast to cross the southern Gulf of Maine and Nova Scotia as a remnant low on Tuesday. The new NHC track forecast is a little to the west and south of the previous advisory track, and lies close to the tightly packed simple- and corrected-consensus track models. Little change in strength is expected until Henri makes landfall in the Rhode Island-eastern Connecticut area this afternoon. After landfall, rapid weakening is forecast due to land interaction and entrainment of cooler air coming in off of the Atlantic Ocean. Henri should weaken to a tropical depression by early Monday, and become post-tropical by Monday afternoon or evening. Due to the degraded radar presentation of Henri, hourly Tropical Cyclone Updates (TCU) will be discontinued after the 1100 AM EDT advisory. Key Messages: 1. Dangerous storm surge inundation is expected to continue today in portions of Long Island, Connecticut, Rhode Island, and southeastern Massachusetts, where a Storm Surge Warning has been issued. Residents in these areas should follow any advice given by local officials. 2. Tropical storm conditions will continue in portions of the tropical storm warning area into tonight. 3. Heavy rainfall may lead to considerable flash, urban, and small stream flooding, along with the potential for widespread minor to isolated moderate river flooding over portions of Long Island, New England, eastern New York, New Jersey and northeast Pennsylvania. 4. Swells from Henri will continue to affect much of the east coast of the U.S. during the next day or so. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 41.1N 71.6W 50 KT 60 MPH 12H 23/0000Z 42.4N 73.2W 35 KT 40 MPH...INLAND 24H 23/1200Z 43.0N 72.7W 30 KT 35 MPH...INLAND 36H 24/0000Z 43.3N 71.3W 25 KT 30 MPH...POST-TROP/INLAND 48H 24/1200Z 43.7N 68.7W 25 KT 30 MPH...POST-TROP/INLAND 60H 25/0000Z 44.3N 64.5W 25 KT 30 MPH...POST-TROPICAL 72H 25/1200Z...DISSIPATED $$ Forecaster Stewart

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Hurricane Henri Forecast Discussion Number 26

2021-08-22 11:06:19| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sun Aug 22 2021 000 WTNT43 KNHC 220905 CCA TCDAT3 Hurricane Henri Discussion Number 26...Corrected NWS National Hurricane Center Miami FL AL082021 500 AM EDT Sun Aug 22 2021 Henri's satellite presentation has remained largely unchanged overnight and early this morning. Deep convection remains over the center and NWS Doppler radar imagery has revealed a convection band that wraps around the circulation forming a loose banding-eye feature. An Air Force Reserve Hurricane Hunter aircraft that has been in the storm for much of the night has reported that the pressure is slightly lower than earlier, around 986 mb, but the flight-level and SFMR winds are not quite as high as before. The initial intensity is maintained at 65 kt for this advisory. The current reconnaissance mission will be in Henri for a few more hours and should provide additional information on the storm's intensity. Henri has been moving just west of due north or 350/15 kt. The storm is expected to move north-northwestward today around the northeastern portion of a cut-off low over the central Appalachians. Some deceleration is indicated by the model guidance, but this motion should bring the center near the eastern portion of Long Island and into southern New England later this morning or early this afternoon. There is still a little spread in the track guidance regarding the landfall point, but the updated NHC forecast lies very close to the previous advisory for the first 12 hours, and is between the multi-model consensus aids and the ECMWF and GFS which are slightly to the left. Regardless of the exact landfall location, storm surge, rainfall, and wind hazards will extend far from the center. After landfall, Henri should slow down and turn east-northeastward on Monday as it becomes embedded in the southern extent of the mid-latitude westerlies. The guidance envelope has shifted a little westward from 24 to 48 hours, and the NHC forecast has been adjusted accordingly. Henri has moved north of the north wall of the Gulf Stream and will encounter cooler waters on its approach to New England. Although some slight weakening is possible, Henri is expected to at or near hurricane strength when it reaches the coast of southern New England. Even if slight weakening does occur it will have little difference on the expected storm surge, wind, and rainfall impacts. Rapid weakening should occur after landfall. Henri is expected to weaken to a tropical depression by early Monday, and become post-tropical shortly thereafter. With the center within radar range and fairly well trackable, hourly Tropical Cyclone Updates will be issued beginning at 600 AM EDT (1000 UTC) to provide updates on Henri's center location. These updates will continue as long as the center remains trackable in radar imagery. Key Messages: 1. Dangerous storm surge inundation is expected to begin this morning in portions of Long Island, Connecticut, Rhode Island, and southeastern Massachusetts, where a Storm Surge Warning has been issued. Residents in these areas should follow any advice given by local officials. 2. Hurricane conditions are expected to begin this morning in portions of Long Island, Connecticut, and Rhode Island, where a Hurricane Warning is in effect. Tropical storm conditions will begin in these areas within the next couple of hours. 3. Heavy rainfall may lead to considerable flash, urban, and small stream flooding, along with the potential for widespread minor to isolated moderate river flooding over portions of Long Island, New England, eastern New York and New Jersey. 4. Swells from Henri will continue to affect much of the east coast of the U.S. during the next day or so. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 40.1N 71.2W 65 KT 75 MPH 12H 22/1800Z 41.5N 71.7W 60 KT 70 MPH...INLAND 24H 23/0600Z 42.7N 72.4W 30 KT 35 MPH...INLAND 36H 23/1800Z 43.5N 72.3W 25 KT 30 MPH...POST-TROP/INLAND 48H 24/0600Z 43.8N 70.5W 25 KT 30 MPH...POST-TROP/INLAND 60H 24/1800Z 44.2N 67.3W 25 KT 30 MPH...POST-TROPICAL 72H 25/0600Z...DISSIPATED $$ Forecaster Brown

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