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Tropical Storm Linda Forecast Discussion Number 38

2021-08-19 16:36:48| Tropical Depression LIDIA

Issued at 500 AM HST Thu Aug 19 2021

Tropical Storm Henri Forecast Discussion Number 15

2021-08-19 16:35:47| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Thu Aug 19 2021 000 WTNT43 KNHC 191435 TCDAT3 Tropical Storm Henri Discussion Number 15 NWS National Hurricane Center Miami FL AL082021 1100 AM EDT Thu Aug 19 2021 Henri is not as well organized as it was yesterday. Microwave images show that the vortex is titled to the south with height due to about 25 kt of north-northeasterly wind shear. The system is still producing a fair amount of deep convection, however, and the cloud pattern resembles a central dense overcast with banding features limited to the south side of the circulation. The Dvorak estimates continue to range from 55 kt to 65 kt, and therefore, the initial intensity is again held at 60 kt. The Air Force Reserve Hurricane Hunters will be investigating Henri later today, and the data the aircraft collects will be very helpful in assessing the storm's structure and strength. The tropical storm is moving just south of due west at 9 kt. Henri is expected to move generally westward through tonight as the storm remains on the south side of a mid-level ridge. On Friday, however, a trough is expected to cut off over the Ohio Valley and mid-Atlantic region of the U.S. while a ridge amplifies to the east of Henri over the western Atlantic. A combination of these features should cause Henri to turn northward on Friday and accelerate in that direction over the weekend. By early next week, the ridge is expected to weaken, which should cause Henri to turn more toward the east. The models are in much better agreement than they were yesterday and their solutions are clustering around southern New England on Sunday and Monday. The NHC track forecast is just a tad to the left of the previous one and lies near the typically best-performing models, the various consensus aids. In addition to the Air Force aircraft that flies through the storm, the NOAA Gulfstream IV jet will also be flying around Henri later today to help assess the environmental conditions and gather data for the numerical models. It is hoped that these data will help the models more accurately predict the future track of the storm. The current north-northeasterly shear over Henri is forecast to continue for about another day, and given the degraded structure of the system it seems unlikely that the storm will strengthen during that time period. However, the shear is expected to decrease on Friday and it will remain quite low through the weekend. Therefore, strengthening to a hurricane is expected during that time period. Once Henri crosses the north wall of the Gulf Stream in a few days, steady weakening is predicted. The NHC intensity forecast is just an update of the previous one and lies near the middle of the guidance envelope. It should be noted that as Henri gains latitude and moves near New England, the wind field is expected to expand. Therefore, 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. Watches will likely be required for portions of this area on Friday. 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. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 29.5N 70.5W 60 KT 70 MPH 12H 20/0000Z 29.7N 71.9W 60 KT 70 MPH 24H 20/1200Z 30.4N 72.9W 60 KT 70 MPH 36H 21/0000Z 31.9N 72.9W 65 KT 75 MPH 48H 21/1200Z 34.4N 72.0W 75 KT 85 MPH 60H 22/0000Z 37.3N 70.7W 80 KT 90 MPH 72H 22/1200Z 39.6N 70.0W 75 KT 85 MPH 96H 23/1200Z 41.6N 69.7W 55 KT 65 MPH 120H 24/1200Z 42.3N 67.0W 45 KT 50 MPH $$ Forecaster Cangialosi

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Hurricane Grace Forecast Discussion Number 24

2021-08-19 10:55:45| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Thu Aug 19 2021 000 WTNT42 KNHC 190855 TCDAT2 Hurricane Grace Discussion Number 24 NWS National Hurricane Center Miami FL AL072021 400 AM CDT Thu Aug 19 2021 After a brief convective hiatus between 0400-0700 UTC, deep convection in the inner-core region has increased and become better organized during the past couple of hours. An Air Force Reserve Hurricane Hunter aircraft investigating Grace more than 4 hours ago reported a central pressure of 986 mb -- down 2 mb from previous passes -- and a maximum 700-mb flight-level wind speed of 74 kt on its last leg northbound around 0500 UTC. The 74-kt flight-level wind equates to about a 67-kt surface wind speed. These data supported maintaining a 70-kt intensity at 0600 UTC. The upper-level outflow remains symmetrical and has been expanding somewhat over the past few hours. The initial motion is 280/15 kt based on the earlier recon fixes and passive microwave satellite data. Grace should continue to move generally westward for the next 48 hours, crossing the coast of the eastern Yucatan Peninsula within the next couple of hours, followed by a track across the Yucatan and emergence over the Bay of Campeche by 24 hours, with a subsequent landfall along the eastern coast of mainland Mexico shortly after the 48-hour forecast period. This track scenario is consistent with the latest 0000 UTC global and regional models, which show the strong deep-layer ridge to the north of Grace maintaining its expansive presence across the western Atlantic, Gulf of Mexico, and northern Mexico. After the second landfall, Grace is expected to turn west-southwestward and dissipate over the mountains of central Mexico by 72 hours. The new NHC forecast track is similar to the previous advisory track, and lies along the northern edge of the tightly packed consensus track models. Given the recent improvement in Grace's inner-core convective structure noted in high-resolution infrared satellite imagery, some slight strengthening to 75 kt could still occur just prior to landfall this morning. Weakening will commence once Grace moves inland over Yucatan, with re-strengthening expected after the cyclone emerges over the Bay of Campeche where the vertical wind shear is forecast to decrease below 10 kt. Grace is expected to be a hurricane when the second landfall occurs along the coast of mainland Mexico, with the cyclone possibly reaching a peak intensity of 75 kt shortly after the 48-hour period. After final landfall in mainland Mexico, Grace should quickly weaken and dissipate over the mountains of Mexico by 72 hours, if not sooner. The remnants of Grace are expected to emerge over the eastern North Pacific and possibly re-develop there, but the uncertainty of whether this will be the original center or a new center precludes forecast points over the Pacific at this time. A Hurricane Warning will likely be required for portions of the Hurricane Watch area of mainland Mexico later this morning or afternoon. Key Messages: 1. Hurricane conditions and a dangerous storm surge are expected in portions of the Hurricane Warning area in the eastern Yucatan Peninsula of Mexico during the next several hours. Preparations to protect life and property should be rushed to completion. 2. There is an increasing risk of hurricane conditions and dangerous storm surge in portions of eastern mainland Mexico beginning late Friday, and a Hurricane Watch is in effect for part of this area. 3. Through the weekend, heavy rainfall across central and northern portions of the Yucatan Peninsula and Veracruz State should lead to flash and urban flooding. In addition, the heavy rainfall from Grace will be capable of producing mudslides in Veracruz. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 20.0N 87.2W 70 KT 80 MPH 12H 19/1800Z 20.3N 89.7W 50 KT 60 MPH...INLAND 24H 20/0600Z 20.6N 92.6W 60 KT 70 MPH...OVER WATER 36H 20/1800Z 20.5N 95.0W 70 KT 80 MPH 48H 21/0600Z 20.1N 97.3W 55 KT 65 MPH...INLAND 60H 21/1800Z 19.7N 100.1W 20 KT 25 MPH...POST-TROP/INLAND 72H 22/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Henri Forecast Discussion Number 14

2021-08-19 10:54:42| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Aug 19 2021 000 WTNT43 KNHC 190854 TCDAT3 Tropical Storm Henri Discussion Number 14 NWS National Hurricane Center Miami FL AL082021 500 AM AST Thu Aug 19 2021 Compared to microwave images from earlier on Wednesday, GMI microwave data from last evening revealed that Henri's structure had deteriorated somewhat, with convection on the west side of the mid-level eye having mostly dissipated. This degradation is likely the result of strong deep-layer shear and dry air in the mid levels. Satellite intensity estimates have either remained steady or decreased a bit, and Henri's initial intensity is therefore held at 60 kt. This value is supported by two evening scatterometer passes, which had peak winds of 52 kt and 57 kt. The GMI and ASCAT data revealed that the center is slightly farther south than previously estimated, and Henri has been moving south of due west, or 260/8 kt. Water vapor imagery shows a shortwave trough moving across the Great Lakes toward the Ohio Valley, and global models are in agreement that this trough will cut off over the central Appalachians in about 48 hours. As a result, the ridge currently steering Henri westward is expected to relocate over the northern Gulf coast, with the cut-off low causing Henri to accelerate northward between Bermuda and the east coast of the United States by late Friday through Sunday. Then, mid-level ridging over Quebec is likely to cause Henri to slow down considerably in the vicinity of southeastern New England or the adjacent offshore waters by Monday. The latest suite of deterministic track models have much less spread compared to on Wednesday, with fairly good agreement on the scenario described above. However, both the GEFS and ECMWF ensembles continue to show a wider assortment of solutions, with stronger storms tending to move closer to the U.S. coast and weaker storms moving farther offshore. With the tight clustering of the current guidance, the trajectory of the new NHC track forecast was not changed much from the previous iteration, although it is a little faster during the time that Henri accelerates to the north. The biggest point here is that it's still too soon to know exactly how close Henri's center will get to the coast of New England. The north-northeasterly shear affecting Henri is not expected to abate for another 24-36 hours. Once the shear does decrease, however, warm waters should foster strengthening, up until Sunday when Henri is expected to move north of the Gulf Stream. An increase in southerly shear and Henri's slow motion over the colder waters off New England should then cause weakening on days 4 and 5. The NHC intensity forecast is a little below the HCCA and IVCN consensus aids, which are being influenced by the seemingly over-aggressive HWRF and COAMPS-TC models, and this new forecast is very similar to the previous prediction. Key Messages: 1. Henri is forecast to be near the northeast coast of the U.S. late this weekend and early next week, and the risks of storm surge, wind, and rain impacts in portions of the northeastern U.S. and Atlantic Canada remains a distinct possibility. Interests in these areas should closely follow the progress of Henri and check for updates to the forecast. 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. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 29.5N 69.5W 60 KT 70 MPH 12H 19/1800Z 29.5N 70.9W 60 KT 70 MPH 24H 20/0600Z 29.9N 72.4W 60 KT 70 MPH 36H 20/1800Z 31.0N 73.0W 65 KT 75 MPH 48H 21/0600Z 33.0N 72.5W 75 KT 85 MPH 60H 21/1800Z 35.7N 71.4W 80 KT 90 MPH 72H 22/0600Z 38.2N 70.2W 80 KT 90 MPH 96H 23/0600Z 41.1N 69.3W 60 KT 70 MPH 120H 24/0600Z 42.0N 67.5W 50 KT 60 MPH $$ Forecaster Berg

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