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Tropical Storm Victor Forecast Discussion Number 4

2021-09-30 10:42:56| National Hurricane Center (Atlantic)

Issued at 800 AM CVT Thu Sep 30 2021 000 WTNT45 KNHC 300842 TCDAT5 Tropical Storm Victor Discussion Number 4 NWS National Hurricane Center Miami FL AL202021 800 AM CVT Thu Sep 30 2021 Victor is gradually getting better organized. AMSR2 microwave data from 0300 UTC showed that the low-level circulation has become more defined, with most convective banding features located west and southwest of the center. Victor's intensity is now estimated to be 40 kt based on Dvorak estimates of T3.0 and T2.5 from TAFB and SAB, respectively, and objective numbers from UW-CIMSS around 40 kt. Victor's vector is toward the west-northwest (290 degrees) at 11 kt, and this heading should continue for the next 36 hours while the storm is located to the south a deep-layer ridge located over the subtropical eastern and central Atlantic. In about 2 days, a mid- to upper-level low is forecast to develop over the central Atlantic, causing Victor to curve around the western periphery of the ridge, which gets shunted eastward between the Azores and the Canary Islands. The track models are in generally good agreement on this scenario, and most of them are clustered tightly among each other. Two notable exceptions, which are discounted at this time, are the HWRF and ECMWF models. The HWRF, which is stronger than the other models, is way off to the east, while the ECMWF lies off to the south and west, a tendency that we've observed recently with other storms in the deep tropics. The NHC track forecast is not changed much from the previous iteration and lies close to the GFS, HCCA, Florida State Superensemble, and TVCA solutions. If the low-level circulation is in fact becoming better defined as shown by microwave imagery, Victor should be able to continue strengthening for the next couple of days in an environment of low vertical shear and over warm waters of roughly 28 degrees Celsius. The NHC intensity forecast is near the upper end of the guidance during this period and continues to show Victor reaching hurricane strength in about 36 hours. Once the aforementioned mid- to upper-level low forms, strong southerly to southwesterly deep-layer shear is expected to develop over Victor and induce a weakening trend in about 3 days. The intensity forecast has been lowered a bit during the latter part of the forecast period given the trends in the intensity models, but it is not as low as the HCCA and IVCN aids. Interestingly, many of the global models suggest that the shear could be so strong that Victor might weaken to a depression or even degenerate into a remnant low by day 5. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 8.7N 27.3W 40 KT 45 MPH 12H 30/1800Z 9.4N 28.8W 50 KT 60 MPH 24H 01/0600Z 10.2N 30.6W 60 KT 70 MPH 36H 01/1800Z 11.2N 32.3W 65 KT 75 MPH 48H 02/0600Z 12.6N 33.8W 65 KT 75 MPH 60H 02/1800Z 14.4N 35.3W 60 KT 70 MPH 72H 03/0600Z 16.6N 37.0W 55 KT 65 MPH 96H 04/0600Z 22.0N 40.2W 40 KT 45 MPH 120H 05/0600Z 27.3N 41.9W 35 KT 40 MPH $$ Forecaster Berg

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Tropical Storm Victor Forecast Advisory Number 4

2021-09-30 10:42:37| National Hurricane Center (Atlantic)

Issued at 0900 UTC THU SEP 30 2021 000 WTNT25 KNHC 300842 TCMAT5 TROPICAL STORM VICTOR FORECAST/ADVISORY NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL202021 0900 UTC THU SEP 30 2021 THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT. TROPICAL STORM CENTER LOCATED NEAR 8.7N 27.3W AT 30/0900Z POSITION ACCURATE WITHIN 30 NM PRESENT MOVEMENT TOWARD THE WEST-NORTHWEST OR 290 DEGREES AT 11 KT ESTIMATED MINIMUM CENTRAL PRESSURE 1004 MB MAX SUSTAINED WINDS 40 KT WITH GUSTS TO 50 KT. 34 KT....... 50NE 0SE 0SW 40NW. 12 FT SEAS..150NE 105SE 0SW 0NW. 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 8.7N 27.3W AT 30/0900Z AT 30/0600Z CENTER WAS LOCATED NEAR 8.5N 26.8W FORECAST VALID 30/1800Z 9.4N 28.8W MAX WIND 50 KT...GUSTS 60 KT. 50 KT... 30NE 0SE 0SW 0NW. 34 KT... 90NE 50SE 30SW 60NW. FORECAST VALID 01/0600Z 10.2N 30.6W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 30NE 20SE 0SW 30NW. 34 KT...100NE 60SE 40SW 70NW. FORECAST VALID 01/1800Z 11.2N 32.3W MAX WIND 65 KT...GUSTS 80 KT. 64 KT... 15NE 0SE 0SW 0NW. 50 KT... 30NE 20SE 10SW 30NW. 34 KT...100NE 70SE 40SW 80NW. FORECAST VALID 02/0600Z 12.6N 33.8W MAX WIND 65 KT...GUSTS 80 KT. 64 KT... 15NE 10SE 0SW 0NW. 50 KT... 30NE 30SE 20SW 20NW. 34 KT... 90NE 70SE 40SW 70NW. FORECAST VALID 02/1800Z 14.4N 35.3W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 30NE 20SE 20SW 20NW. 34 KT... 80NE 70SE 30SW 60NW. FORECAST VALID 03/0600Z 16.6N 37.0W MAX WIND 55 KT...GUSTS 65 KT. 50 KT... 30NE 20SE 0SW 20NW. 34 KT... 70NE 70SE 30SW 50NW. 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 04/0600Z 22.0N 40.2W MAX WIND 40 KT...GUSTS 50 KT. OUTLOOK VALID 05/0600Z 27.3N 41.9W MAX WIND 35 KT...GUSTS 45 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 8.7N 27.3W NEXT ADVISORY AT 30/1500Z $$ FORECASTER BERG

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Hurricane Sam Forecast Discussion Number 30

2021-09-30 04:56:52| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Sep 29 2021 000 WTNT43 KNHC 300256 TCDAT3 Hurricane Sam Discussion Number 30 NWS National Hurricane Center Miami FL AL182021 1100 PM AST Wed Sep 29 2021 Sam is intensifying tonight after completing an eyewall replacement cycle. A recent NOAA Hurricane Hunter aircraft showed peak 700 mb flight-level winds of 138 kt, multiple SFMR surface winds of 120 kt or greater, plus falling central pressure to about 940 mb. This deepening trend is also seen on recent satellite imagery, with significant warming within the eye noted. These data support raising the initial intensity to 125 kt for this advisory. It is of note that the NOAA mission has been quite helpful for both the size and intensity analysis, with dropsondes and SFMR data showing that the hurricane has grown quite a bit since earlier today, mostly on the eastern side. Additionally, reflectivity data from the core confirmed the end of the eyewall replacement cycle. The hurricane could strengthen a little more overnight while it moves over a warm ocean eddy in fairly light shear. Afterward, gradually cooling SSTs, falling ocean heat content, and the inevitable future eyewall replacement cycles should cause a weakening trend. However, this will likely not be as steady as shown below, and significant deviations (upward or downward) from the forecast can be expected. Faster weakening is expected by the weekend due to cool SSTs and increasing shear. The new forecast is close to the intensity consensus, and is a little higher than the previous NHC prediction early on, primarily due to the initial wind speed. Sam has sped up tonight, now estimated at 315/10 kt. It sounds like a broken record, but there are no changes to the forecast during the first few days as model guidance is in excellent agreement on a gradually rightward-curving track, passing a couple of hundred n mi or more east of Bermuda. Afterward, guidance is actually in worse agreement over the weekend, with widely divergent solutions from an upper-level trough picking up Sam and turning it north toward Newfoundland or the trough leaving Sam behind, causing a slow eastward motion. The trend in the guidance is for a slower motion at long range, so I've elected to keep the day 4 and 5 points almost the same as the previous advisory, just a hair faster than the latest consensus aids. Key Messages: 1. Swells generated by Sam will impact the Lesser Antilles during the next several days. Swells are expected to reach Bermuda and the Bahamas in a day or so, and then spread to the United States east coast by this weekend. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. 2. A Tropical Storm Watch could be required for Bermuda on Thursday, and interests there should monitor the progress of Sam. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 20.6N 58.4W 125 KT 145 MPH 12H 30/1200Z 21.9N 59.6W 130 KT 150 MPH 24H 01/0000Z 24.1N 60.9W 125 KT 145 MPH 36H 01/1200Z 26.8N 61.8W 120 KT 140 MPH 48H 02/0000Z 29.6N 61.8W 115 KT 130 MPH 60H 02/1200Z 32.2N 60.7W 110 KT 125 MPH 72H 03/0000Z 34.3N 59.2W 100 KT 115 MPH 96H 04/0000Z 37.5N 54.5W 85 KT 100 MPH 120H 05/0000Z 42.0N 48.5W 70 KT 80 MPH $$ Forecaster Blake

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Hurricane Sam Forecast Advisory Number 30

2021-09-30 04:52:22| National Hurricane Center (Atlantic)

Issued at 0300 UTC THU SEP 30 2021 000 WTNT23 KNHC 300252 TCMAT3 HURRICANE SAM FORECAST/ADVISORY NUMBER 30 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182021 0300 UTC THU SEP 30 2021 THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT. INTERESTS IN BERMUDA SHOULD MONITOR THE PROGRESS OF SAM. A TROPICAL STORM WATCH COULD BE REQUIRED FOR THE ISLAND ON THURSDAY. HURRICANE CENTER LOCATED NEAR 20.6N 58.4W AT 30/0300Z POSITION ACCURATE WITHIN 15 NM PRESENT MOVEMENT TOWARD THE NORTHWEST OR 315 DEGREES AT 10 KT ESTIMATED MINIMUM CENTRAL PRESSURE 940 MB EYE DIAMETER 15 NM MAX SUSTAINED WINDS 125 KT WITH GUSTS TO 150 KT. 64 KT....... 55NE 45SE 40SW 45NW. 50 KT....... 90NE 60SE 60SW 70NW. 34 KT.......130NE 120SE 90SW 100NW. 12 FT SEAS..180NE 135SE 150SW 180NW. 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 20.6N 58.4W AT 30/0300Z AT 30/0000Z CENTER WAS LOCATED NEAR 20.3N 58.0W FORECAST VALID 30/1200Z 21.9N 59.6W MAX WIND 130 KT...GUSTS 160 KT. 64 KT... 55NE 45SE 40SW 45NW. 50 KT... 90NE 60SE 60SW 70NW. 34 KT...130NE 120SE 90SW 100NW. FORECAST VALID 01/0000Z 24.1N 60.9W MAX WIND 125 KT...GUSTS 150 KT. 64 KT... 50NE 45SE 35SW 45NW. 50 KT... 90NE 60SE 60SW 70NW. 34 KT...130NE 130SE 90SW 100NW. FORECAST VALID 01/1200Z 26.8N 61.8W MAX WIND 120 KT...GUSTS 145 KT. 64 KT... 50NE 45SE 35SW 40NW. 50 KT... 80NE 60SE 60SW 60NW. 34 KT...130NE 140SE 90SW 100NW. FORECAST VALID 02/0000Z 29.6N 61.8W MAX WIND 115 KT...GUSTS 140 KT. 64 KT... 50NE 50SE 40SW 40NW. 50 KT... 80NE 80SE 60SW 70NW. 34 KT...140NE 150SE 110SW 110NW. FORECAST VALID 02/1200Z 32.2N 60.7W MAX WIND 110 KT...GUSTS 135 KT. 50 KT... 80NE 80SE 60SW 70NW. 34 KT...140NE 150SE 110SW 130NW. FORECAST VALID 03/0000Z 34.3N 59.2W MAX WIND 100 KT...GUSTS 120 KT. 50 KT... 80NE 80SE 70SW 80NW. 34 KT...140NE 160SE 130SW 150NW. 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 04/0000Z 37.5N 54.5W MAX WIND 85 KT...GUSTS 105 KT. OUTLOOK VALID 05/0000Z 42.0N 48.5W MAX WIND 70 KT...GUSTS 85 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 20.6N 58.4W NEXT ADVISORY AT 30/0900Z $$ FORECASTER BLAKE

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Tropical Storm Victor Forecast Discussion Number 3

2021-09-30 04:47:28| National Hurricane Center (Atlantic)

Issued at 200 AM CVT Thu Sep 30 2021 000 WTNT45 KNHC 300247 TCDAT5 Tropical Storm Victor Discussion Number 3 NWS National Hurricane Center Miami FL AL202021 200 AM CVT Thu Sep 30 2021 Victor has changed little in organization since the last advisory, with a large circulation and a complex of convective bands mainly in the northern semicircle. Satellite intensity estimates from TAFB and SAB remain at or near 35 kt, as do other objective intensity estimates. Thus, the initial intensity is still 35 kt, although the most recent ASCAT-A data suggests the possibility that this is a little generous. The center has moved or re-formed a bit to the west during the past several hours, although the longer-term motion still seems to be to the west-northwest at 290/11 kt. Other than the more westerly initial position, there is little change to the forecast philosophy or the forecast track since the last advisory. Victor is forecast to move west-northwestward for the next 36 h or so as it is steered by the flow on the south side of a deep-layer ridge. By 48 h, the global models forecast the western periphery of the ridge to get eroded by to a mid- to upper-level low over the subtropical central Atlantic. This evolution should cause the cyclone to turn northwestward at that time, followed by a northward turn by the end of the forecast period. There remains a fair amount of spread in the timing and location of the northward turn with the GFS and HWRF still on the right side of the guidance envelope and the ECMWF showing the slowest and westernmost solution. The new forecast track is in the center of the guidance envelope and lies very close to the various consensus models. For the next 36-48 h, Victor is expected to remain in an environment of warm sea surface temperatures and light vertical wind shear. This should allow steady strengthening, and rapid strengthening cannot be ruled out if the storm develops a better defined inner core. Based on a steady strengthening scenario, the new intensity forecast is identical to the previous one, taking Victor to hurricane intensity in 36 h with a peak intensity of 70 kt in 48 h. After that time, the aforementioned upper-level low is expected to cause significant shear over Victor while the cyclone moves into a drier air mass. This combination should cause the cyclone to weaken, and it is possible Victor could weaken faster than currently forecast after 60 hours. The new official intensity forecast lies near the upper edge of the intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 8.4N 26.7W 35 KT 40 MPH 12H 30/1200Z 8.9N 28.3W 45 KT 50 MPH 24H 01/0000Z 9.7N 30.2W 55 KT 65 MPH 36H 01/1200Z 10.6N 32.0W 65 KT 75 MPH 48H 02/0000Z 11.8N 33.5W 70 KT 80 MPH 60H 02/1200Z 13.4N 35.1W 70 KT 80 MPH 72H 03/0000Z 15.5N 36.7W 60 KT 70 MPH 96H 04/0000Z 20.5N 39.5W 45 KT 50 MPH 120H 05/0000Z 26.0N 41.0W 40 KT 45 MPH $$ Forecaster Beven

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