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Hurricane Sam Forecast Discussion Number 46
2021-10-04 04:34:16| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Oct 03 2021 000 WTNT43 KNHC 040234 TCDAT3 Hurricane Sam Discussion Number 46 NWS National Hurricane Center Miami FL AL182021 1100 PM AST Sun Oct 03 2021 Sam still had a surprise up its sleeve tonight, with its eye becoming warmer on satellite images along with a stronger eyewall. Microwave data from earlier today indicated that Sam has been undergoing a concentric eyewall cycle, and it appears that the inner eyewall has become better defined. Regardless, it is not every day you see a hurricane with that clear of an eye near 40N, and the intensity estimates the evening range from 90-100 kt. Given the concentric eyewalls, the initial wind speed is conservatively raised to 90 kt, but it could be higher. High-resolution NOAA OISST data indicate that Sam is moving near a warm eddy along the north wall of the Gulf Stream. This favorable factor, in addition to low shear, should keep Sam's weakening to a minimum in the near term. Later on, although the shear increases rapidly and SSTs fall quickly, Sam is expected to transition into a powerful extratropical cyclone late Monday or early Tuesday due to a mid-latitude trough interaction well east of Newfoundland. This should cause extratropical Sam to maintain hurricane-force winds until early Wednesday. A slow weakening is expected thereafter as it slowly spins down as an occluded low. No significant changes were made to the previous forecast. Sam is moving faster, now 050/17 kt. A northeastward motion and continued acceleration is forecast through Monday as the cyclone gets caught in southwesterly flow ahead of the mid-latitude trough. The tropical cyclone is expected to be the main surface low center as it merges with the trough in a couple days, hooking briefly to the left. Thereafter, the system should resume a northeastward motion and gradually turn northward and even westward at long range as it moves around another trough. Model guidance is close to the previous cycle, even with the loopy track, and the new NHC forecast is basically just an update of the last advisory. Key Messages: 1. Swells generated by Sam will impact the northern Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, the eastern United States and Atlantic Canada for the next couple of days. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 39.3N 51.2W 90 KT 105 MPH 12H 04/1200Z 41.6N 47.3W 85 KT 100 MPH 24H 05/0000Z 46.5N 42.1W 75 KT 85 MPH 36H 05/1200Z 50.4N 40.3W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 06/0000Z 50.8N 38.3W 65 KT 75 MPH...POST-TROP/EXTRATROP 60H 06/1200Z 51.6N 33.3W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 07/0000Z 54.5N 28.2W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 08/0000Z 61.0N 28.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 09/0000Z 61.5N 32.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Blake
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Tropical Depression Victor Forecast Discussion Number 18
2021-10-03 22:39:43| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sun Oct 03 2021 000 WTNT45 KNHC 032039 TCDAT5 Tropical Depression Victor Discussion Number 18 NWS National Hurricane Center Miami FL AL202021 500 PM AST Sun Oct 03 2021 The convective structure of Victor has deteriorated this afternoon. Only small pulses of convection have been observed north of the center over the past several hours. Victor's exposed low-level circulation is also becoming more diffuse, with multiple cloud swirls noted in visible satellite imagery. Hopefully, scatterometer data this evening will provide more information about whether Victor still possesses a closed and well-defined surface center. For now, Victor is held as a 30-kt tropical depression, which is consistent with earlier scatterometer winds and a blend of the data-T and current intensity Dvorak estimates from TAFB and SAB. Victor is unlikely to remain a tropical cyclone for much longer. The dry mid-level environment and 20-25 kt of southwesterly vertical wind shear are expected to limit Victor's ability to sustain deep, organized convection going forward. Even if another diurnal convective pulse occurs tonight, it should be quickly stripped away from the center by the moderate to strong shear. The official NHC forecast shows Victor becoming a remnant low on Monday, then opening up into a trough and dissipating soon thereafter. Victor is moving northwestward, or 315/11 kt. A northwestward or west-northwestward motion is expected to continue through dissipation as the depression is steered by a subtropical ridge to its northeast. The official NHC track forecast is essentially an update of the previous one. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 17.1N 41.3W 30 KT 35 MPH 12H 04/0600Z 18.4N 42.9W 25 KT 30 MPH 24H 04/1800Z 19.7N 45.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 05/0600Z...DISSIPATED $$ Forecaster Reinhart
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Hurricane Sam Forecast Discussion Number 44
2021-10-03 16:47:32| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Oct 03 2021 000 WTNT43 KNHC 031447 TCDAT3 Hurricane Sam Discussion Number 44 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Sun Oct 03 2021 Sam's cloud pattern remains quite symmetric for a hurricane moving into the higher latitudes. The eye has become more apparent in both visible and infrared satellite imagery over the past few hours. A very timely 1155 UTC GMI microwave image also reveals a well-defined inner eye that was surrounded by an outer ring of convection at a much larger radius. A blend of the T- and CI-numbers from the lastest subjective Dvorak classifications yields an initial intensity of 85 kt, this is also supported by earlier UW/CIMSS SATCON estimates. The vertical shear over Sam is expected to remain low for the next 6-12 hours and only gradual weakening is anticipated while the system moves over gradually decreasing SSTs. Later tonight, Sam is expected to move over much cooler waters north of the north wall of the Gulf Stream and into an area of increasing southwesterly shear, which should result in continued weakening. However, a strong mid-tropospheric trough approaching Sam from the west on Monday is expected to result in a fairly quick transition of Sam to a large and powerful extratropical low. The low is forecast to gradually weaken over the far north Atlantic during the middle to latter portions of the week as the baroclinic forcing decreases. The latest NHC intensity forecast is similar to the previous advisory and is a blend of the various intensity aids during the early portion of the period, but leans toward the global model guidance during the post-tropical phase. Sam is moving northeastward or 050/14 kt. The cyclone should continue to move northeastward in the flow between a strong subtropical ridge over the eastern Atlantic and mid-latitude trough over Atlantic Canada. As this trough approaches Sam from the west, a much faster northeastward motion is expected by Monday and Monday night. Around midweek, the post-tropical cyclone is forecast to slow down as it rotates around a large cut-off low over the north Atlantic. After that time, the low is forecast to resume a northeastward motion before it slows once again to the southwest of Iceland. Given the future complex interactions of the post-tropical low with the cut-off low and trough over the north Atlantic, the track guidance is in surprisingly good agreement, and the NHC forecast is near a blend of the ECMWF and GFS global models. Key Messages: 1. Swells generated by Sam will impact the northern Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, the eastern United States and Atlantic Canada for the next couple of days. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 37.7N 54.6W 85 KT 100 MPH 12H 04/0000Z 39.3N 51.9W 80 KT 90 MPH 24H 04/1200Z 42.4N 47.0W 75 KT 85 MPH 36H 05/0000Z 47.0N 41.7W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 05/1200Z 50.9N 39.8W 65 KT 75 MPH...POST-TROP/EXTRATROP 60H 06/0000Z 50.9N 38.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 06/1200Z 51.5N 33.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 07/1200Z 59.2N 27.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 08/1200Z 60.5N 31.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown
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Tropical Depression Victor Forecast Discussion Number 17
2021-10-03 16:40:59| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Oct 03 2021 000 WTNT45 KNHC 031440 TCDAT5 Tropical Depression Victor Discussion Number 17 NWS National Hurricane Center Miami FL AL202021 1100 AM AST Sun Oct 03 2021 Despite persistent southwesterly vertical wind shear, Victor has managed to maintain an area of deep convection to the northeast of its low-level center through the morning hours. The latest objective and subjective satellite estimates range from 30-35 kt. However, an ASCAT-A pass from 1110 UTC indicates the increasingly elongated center of Victor is about 45 n mi south of previous estimates, which puts the center farther away from the edge of the convective overcast. Although a few 35-kt ASCAT wind vectors are noted, these retrievals are collocated with the most intense convection and appear artificially high when compared to the surrounding 20 to 30-kt wind field. Thus, the initial intensity of Victor is held at 30 kt for this advisory. The SHIPS guidance indicates 15-20 kt of vertical wind shear will persist over Victor today, with even stronger shear expected on Monday. Additionally, the dry mid-level environment that Victor is embedded within appears unfavorable for sustaining deep convection. Therefore, gradual weakening is expected early this week, and Victor is forecast to lose its convection and degenerate into a remnant low by late Monday. Another plausible scenario is that Victor's low-level center continues to lose definition and the system opens up into a trough with the next couple of days. Either way, Victor does not appear to have much of a future. A subtropical ridge over the eastern Atlantic is steering Victor northwestward, or 310/10 kt. A northwestward motion is expected to continue through dissipation as Victor moves around the southwestern periphery of the subtropical ridge. Although the track reasoning has not changed, the official NHC forecast track lies to the left of the previous advisory due to the center relocation described above. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 16.1N 40.3W 30 KT 35 MPH 12H 04/0000Z 17.6N 41.9W 30 KT 35 MPH 24H 04/1200Z 19.5N 43.9W 25 KT 30 MPH 36H 05/0000Z 21.1N 45.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 05/1200Z 22.4N 48.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 06/0000Z...DISSIPATED $$ Forecaster Reinhart
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Tropical Depression Victor Forecast Discussion Number 16
2021-10-03 10:58:57| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Oct 03 2021 000 WTNT45 KNHC 030858 TCDAT5 Tropical Depression Victor Discussion Number 16 NWS National Hurricane Center Miami FL AL202021 500 AM AST Sun Oct 03 2021 Victor remains a sheared tropical cyclone with intense deep convection having developed closer to the center in the northeastern quadrant since the previous advisory. Satellite intensity estimates remain at T2.0/30 kt, so the advisory intensity remains at 30 kt. It is possible that Victor could have regained tropical storm status based on the robust convective shear pattern. For now, however, Victor will remain a depression until new ASCAT surface wind data arrive later this morning. Some fluctuations in intensity could occur this morning due to the aforementioned better defined shear pattern. By tonight, however, weakening is anticipated as Victor encounters southwesterly vertical wind shear in excess of 25 kt and moves into a drier air mass, which will act to decrease both the depth and amount of inner-core deep convection. Victor is expected to gradually spin down tonight and Monday, with the circulation opening up into a trough on Tuesday. Victor continues to move northwestward, or 315/14 kt. A motion toward the northwest is forecast to continue as Victor remains embedded within the southeasterly flow around a deep-layer subtropical ridge. The new NHC track forecast is essentially just an update of the previous advisory track, and lies near the tightly clustered consensus track models. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 16.1N 39.9W 30 KT 35 MPH 12H 03/1800Z 17.6N 41.4W 30 KT 35 MPH 24H 04/0600Z 19.6N 43.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 04/1800Z 21.3N 45.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 05/0600Z 22.8N 47.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 05/1800Z 24.3N 49.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 06/0600Z...DISSIPATED $$ Forecaster Stewart
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