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Hurricane Sam Forecast Discussion Number 35

2021-10-01 10:46:48| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Oct 01 2021 000 WTNT43 KNHC 010846 TCDAT3 Hurricane Sam Discussion Number 35 NWS National Hurricane Center Miami FL AL182021 500 AM AST Fri Oct 01 2021 An Air Force Reserve Hurricane Hunter aircraft investigated Sam a few hours ago and found that the already-intense hurricane had strengthened a bit since yesterday afternoon's reconnaissance flight. The plane measured a peak 700-mb flight-level wind of 147 kt in the northeastern eyewall, and using a typical 90-percent reduction from that altitude, the intensity is estimated to be 130 kt. Dropsondes released in the eye also indicated that the central pressure had fallen to 934 mb. This drop in pressure is likely due to a combination of the strengthening and an expansion of the tropical-storm- and hurricane-force wind fields, which was confirmed by the aircraft and scatterometer data from last evening. Sam is moving a little faster toward the north-northwest (345/15 kt) as it curves around the western periphery of a mid-tropospheric ridge located over the eastern and central subtropical Atlantic. The hurricane is expected to turn northward later today and then northeastward by Saturday night--passing well to the east of Bermuda--when it begins to move between the ridge and a mid- to upper-level low located over the northeastern United States and Atlantic Canada. Interaction and a possible merger with the aforementioned low during extratropical transition is likely to cause a sudden north-northeastward acceleration to the southeast of Newfoundland on day 4, followed by a slower motion toward the east-northeast on day 5. The track models are very tightly clustered for much of the 5-day forecast period, yielding high confidence in the NHC track forecast. The new NHC forecast is relatively unchanged from the previous forecast, and closely follows the GFEX and TVCA consensus aids. Although fluctuations in intensity will still be possible, a general weakening trend is anticipated in the coming days as Sam moves over a gradually cooler ocean, reaching sub-26C waters by day 3. However, the weakening is not expected to be rapid due to continued upper-level divergence and only light-to-moderate deep-layer shear, and Sam could remain a major hurricane at least through Saturday night. Global models now indicate that Sam should complete extratropical transition by day 4, and baroclinic forcing is likely to keep the system as a potent hurricane-force post-tropical cyclone through the end of the forecast period. The NHC intensity forecast is essentially an update of the previous forecast, lying close to the HCCA and IVCN consensus aids. Key Messages: 1. Swells generated by Sam will impact the northern Leeward Islands and the Greater Antilles, including Puerto Rico, during the next couple of days. Swells are expected to reach Bermuda and the Bahamas today, and then spread to the United States east coast and Atlantic Canada this weekend. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. 2. Tropical storm conditions are expected on Bermuda beginning tonight or early Saturday, and a Tropical Storm Warning is in effect for the island. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 26.6N 61.7W 130 KT 150 MPH 12H 01/1800Z 28.8N 62.0W 125 KT 145 MPH 24H 02/0600Z 31.7N 61.2W 115 KT 130 MPH 36H 02/1800Z 34.2N 59.7W 105 KT 120 MPH 48H 03/0600Z 36.0N 57.8W 95 KT 110 MPH 60H 03/1800Z 37.7N 55.0W 90 KT 105 MPH 72H 04/0600Z 40.1N 51.4W 85 KT 100 MPH 96H 05/0600Z 47.7N 44.8W 75 KT 85 MPH...POST-TROP/EXTRATROP 120H 06/0600Z 50.1N 38.1W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg

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Hurricane Sam Forecast Advisory Number 35

2021-10-01 10:45:19| National Hurricane Center (Atlantic)

Issued at 0900 UTC FRI OCT 01 2021 000 WTNT23 KNHC 010845 TCMAT3 HURRICANE SAM FORECAST/ADVISORY NUMBER 35 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182021 0900 UTC FRI OCT 01 2021 CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY... NONE. SUMMARY OF WATCHES AND WARNINGS IN EFFECT... A TROPICAL STORM WARNING IS IN EFFECT FOR... * BERMUDA A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS. HURRICANE CENTER LOCATED NEAR 26.6N 61.7W AT 01/0900Z POSITION ACCURATE WITHIN 15 NM PRESENT MOVEMENT TOWARD THE NORTH-NORTHWEST OR 345 DEGREES AT 15 KT ESTIMATED MINIMUM CENTRAL PRESSURE 934 MB EYE DIAMETER 25 NM MAX SUSTAINED WINDS 130 KT WITH GUSTS TO 160 KT. 64 KT....... 60NE 50SE 35SW 40NW. 50 KT....... 90NE 80SE 50SW 60NW. 34 KT.......150NE 140SE 90SW 110NW. 12 FT SEAS..270NE 180SE 210SW 240NW. 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 26.6N 61.7W AT 01/0900Z AT 01/0600Z CENTER WAS LOCATED NEAR 25.8N 61.6W FORECAST VALID 01/1800Z 28.8N 62.0W MAX WIND 125 KT...GUSTS 150 KT. 64 KT... 60NE 50SE 40SW 40NW. 50 KT... 90NE 80SE 60SW 60NW. 34 KT...150NE 150SE 100SW 110NW. FORECAST VALID 02/0600Z 31.7N 61.2W MAX WIND 115 KT...GUSTS 140 KT. 64 KT... 55NE 50SE 40SW 40NW. 50 KT... 80NE 80SE 60SW 60NW. 34 KT...150NE 160SE 120SW 130NW. FORECAST VALID 02/1800Z 34.2N 59.7W MAX WIND 105 KT...GUSTS 130 KT. 64 KT... 50NE 50SE 40SW 40NW. 50 KT... 80NE 80SE 70SW 70NW. 34 KT...160NE 170SE 140SW 150NW. FORECAST VALID 03/0600Z 36.0N 57.8W MAX WIND 95 KT...GUSTS 115 KT. 64 KT... 50NE 50SE 50SW 40NW. 50 KT... 80NE 80SE 70SW 70NW. 34 KT...160NE 180SE 160SW 170NW. FORECAST VALID 03/1800Z 37.7N 55.0W MAX WIND 90 KT...GUSTS 110 KT. 50 KT... 80NE 90SE 80SW 70NW. 34 KT...170NE 190SE 180SW 180NW. FORECAST VALID 04/0600Z 40.1N 51.4W MAX WIND 85 KT...GUSTS 105 KT. 50 KT... 80NE 100SE 90SW 80NW. 34 KT...180NE 200SE 200SW 180NW. 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 05/0600Z 47.7N 44.8W...POST-TROP/EXTRATROP MAX WIND 75 KT...GUSTS 90 KT. OUTLOOK VALID 06/0600Z 50.1N 38.1W...POST-TROP/EXTRATROP MAX WIND 65 KT...GUSTS 80 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 26.6N 61.7W INTERMEDIATE PUBLIC ADVISORY...WTNT33 KNHC/MIATCPAT3...AT 01/1200Z NEXT ADVISORY AT 01/1500Z $$ FORECASTER BERG

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Tropical Storm Victor Forecast Discussion Number 8

2021-10-01 10:42:18| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Oct 01 2021 000 WTNT45 KNHC 010842 TCDAT5 Tropical Storm Victor Discussion Number 8 NWS National Hurricane Center Miami FL AL202021 500 AM AST Fri Oct 01 2021 Infrared and microwave satellite imagery indicate that Victor has continued to become a little better organized, with a 0342Z AMSR2 overpass showing that a 75-percent-closed mid-level eye feature had formed. However, both data sources also revealed that a pronounced dry slot has formed in the southeastern quadrant. Upper-level outflow remains well established in all quadrants except to the south where it is somewhat restricted. Despite the slightly improved satellite signatures, subjective and objective intensity classifications have not changed since the previous advisory, so the intensity remains at 50 kt for this advisory. The initial motion estimate is 305/13 kt. Victor has made a slight jog toward the northwest, but this is likely a temporary motion due to redevelopment of the center farther into the convective cloud shield. The cyclone should resume a west-northwestward motion later today and maintain that motion for another day or so as Victor moves along the southwestern periphery of a strong subtropical ridge situated over the east-central Atlantic. The latest model runs continue to show a broad mid- to upper-level low developing over the central Atlantic to the west of Victor in the 24-72-h forecast period, which will act to erode the western portion of the ridge and create a deep-layer southerly flow pattern across the cyclone. As a result, Victor is forecast to turn northwestward by the weekend and then move northward by early next week. Owing to a more robust mid-/upper-level low forecast to develop than previously expected, the latest NHC track guidance has made a significant westward shift by at least 100 nmi at 72 h and nearly 200 nmi on days 4 and 5. This westward shift is due to Victor now forecast to weaken faster and become more vertically shallow, with the dominant steering flow shifting to low-level easterlies. The new NHC track forecast has also been shifted westward, but not as far west as the tightly packed consensus models, all of which lie well to the east of the westernmost GFS solution. Victor is expected to remain in a somewhat favorable environment for the next 18 h or so, which should allow for at least some slight strengthening to occur. Thereafter, however, southwesterly deep-layer vertical wind shear is forecast by the GFS and ECMWF models to increase to 20-25 kt in 24 hours and 30-35 kt by 72 h. These hostile shear conditions, in conjunction with a drier air mass, should result in gradual weakening during the 24-120-h period, with Victor becoming a remnant low on day 5. The new official intensity forecast is a little below the previous advisory, but it is above the consensus intensity models ICON, HCCA, and FSSE, due to the recent development of the aforementioned primitive eye feature. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 11.7N 32.3W 50 KT 60 MPH 12H 01/1800Z 12.4N 33.6W 55 KT 65 MPH 24H 02/0600Z 13.4N 35.3W 55 KT 65 MPH 36H 02/1800Z 14.9N 36.8W 50 KT 60 MPH 48H 03/0600Z 16.7N 38.6W 45 KT 50 MPH 60H 03/1800Z 19.0N 40.5W 40 KT 45 MPH 72H 04/0600Z 21.0N 42.0W 35 KT 40 MPH 96H 05/0600Z 24.0N 44.0W 30 KT 35 MPH 120H 06/0600Z 28.0N 45.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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Tropical Storm Victor Forecast Advisory Number 8

2021-10-01 10:41:51| National Hurricane Center (Atlantic)

Issued at 0900 UTC FRI OCT 01 2021 000 WTNT25 KNHC 010841 TCMAT5 TROPICAL STORM VICTOR FORECAST/ADVISORY NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL202021 0900 UTC FRI OCT 01 2021 THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT. TROPICAL STORM CENTER LOCATED NEAR 11.7N 32.3W AT 01/0900Z POSITION ACCURATE WITHIN 30 NM PRESENT MOVEMENT TOWARD THE NORTHWEST OR 305 DEGREES AT 13 KT ESTIMATED MINIMUM CENTRAL PRESSURE 997 MB MAX SUSTAINED WINDS 50 KT WITH GUSTS TO 60 KT. 50 KT....... 50NE 0SE 0SW 50NW. 34 KT.......140NE 90SE 0SW 100NW. 12 FT SEAS..150NE 90SE 45SW 150NW. 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 11.7N 32.3W AT 01/0900Z AT 01/0600Z CENTER WAS LOCATED NEAR 11.4N 31.7W FORECAST VALID 01/1800Z 12.4N 33.6W MAX WIND 55 KT...GUSTS 65 KT. 50 KT... 50NE 0SE 0SW 50NW. 34 KT...140NE 80SE 30SW 100NW. FORECAST VALID 02/0600Z 13.4N 35.3W MAX WIND 55 KT...GUSTS 65 KT. 50 KT... 50NE 0SE 0SW 50NW. 34 KT...140NE 80SE 30SW 100NW. FORECAST VALID 02/1800Z 14.9N 36.8W MAX WIND 50 KT...GUSTS 60 KT. 50 KT... 40NE 0SE 0SW 0NW. 34 KT...120NE 70SE 30SW 80NW. FORECAST VALID 03/0600Z 16.7N 38.6W MAX WIND 45 KT...GUSTS 55 KT. 34 KT...100NE 60SE 20SW 70NW. FORECAST VALID 03/1800Z 19.0N 40.5W MAX WIND 40 KT...GUSTS 50 KT. 34 KT... 80NE 60SE 0SW 60NW. FORECAST VALID 04/0600Z 21.0N 42.0W MAX WIND 35 KT...GUSTS 45 KT. 34 KT... 60NE 50SE 0SW 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 05/0600Z 24.0N 44.0W MAX WIND 30 KT...GUSTS 40 KT. OUTLOOK VALID 06/0600Z 28.0N 45.0W...POST-TROP/REMNT LOW MAX WIND 25 KT...GUSTS 35 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 11.7N 32.3W NEXT ADVISORY AT 01/1500Z $$ FORECASTER STEWART

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Hurricane Sam Forecast Discussion Number 34

2021-10-01 04:53:43| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Thu Sep 30 2021 000 WTNT43 KNHC 010253 TCDAT3 Hurricane Sam Discussion Number 34 NWS National Hurricane Center Miami FL AL182021 1100 PM AST Thu Sep 30 2021 Sam's satellite structure on infrared remains quite impressive this evening, with a circular eye staying quite warm (+10-20C) in comparison to the ring of cold cloud tops associated with the eyewall (-60 to -70C). The most recent microwave imagery was a SSMIS pass at 1957 UTC, which indicated the eyewall remains quite intense, if just a little asymmetric with a stronger western semicircle. This eyewall asymmetry is consistent with a touch of light southerly shear affecting the cyclone as diagnosed by ECMWF-SHIPS. However, this shear does not appear to be having a significant impact on the hurricane's intensity. While there have not been any recent aircraft data to determine Sam's intensity since the last mission departed the hurricane at around 2000 UTC, the satellite intensity estimates have not changed much this evening. Thus, the initial intensity has been held at 125-kt this advisory. Another Air Force Reserve Reconnaissance Mission will be flying into Sam overnight to get a better sense of the current intensity. Following Sam's eye tonight, the hurricane is beginning to make a gradual turn northward at a faster motion, with the latest estimate now north-northwest at 345/14 kt. The track guidance in the short-term remains in good agreement that Sam should continue to turn to the north, north-northeast, and then northeastward as it is steered around the western edge of a large subtropical ridge over the central Atlantic. This track should take the hurricane east of Bermuda. While there is a large deep-layer trough located north of Sam, this feature will not initially capture the cyclone, as this trough first de-amplifies and merges with a larger deep-layer trough located over the far eastern Provinces of Canada. In fact, Sam's forward motion to the northeast in 48-72 hours may even slow a tad as it remains just south of the stronger upper-level westerlies. However, by 96-120 hours, the deep-layer low over Canada is expected to dig southeastward into North Atlantic, and will likely capture Sam as the hurricane rapidly accelerates ahead of this amplifying trough. It is in the 72-120 hour time-frame that a lot of the track guidance diverges, mostly related to the timing and degree of Sam's interaction of with this trough ejecting out of Canada. For now, the official NHC track forecast has elected to stay close to the track consensus TVCN, which has preformed well with this hurricane so far. This latest track is just a bit northeast and faster than the previous one after 72 hours. Sam still has another 24 hours under warm 28-29 C sea-surface temperatures while the southerly vertical wind shear is expected to remain light. Thus, the hurricane is expected to maintain Category 4 intensity over the next day or so, with short-term intensity changes likely to be controlled by inner core dynamics (such as eyewall replacement cycles). Thereafter, sea surface temperatures decrease markedly as southerly shear is also expected to gradually increase. This combination should lead to steady weakening. After 72 hours, the rate of weakening has actually been slowed a tad, since the ECMWF, GFS, and Canadian models all show Sam receiving significant baroclinic support as it undergoes a dynamic extratropical transition while the hurricane phases with the large baroclinic trough emerging off Canada. Simulated satellite imagery from these models suggest that Sam's transition to an extratropical cyclone should take place between 96-120 hours, with the resulting cyclone producing a large wind footprint across the North Atlantic basin. Key Messages: 1. Swells generated by Sam will impact the Northern Leeward Islands and the Greater Antilles, including Puerto Rico, during the next few days. Swells are expected to reach Bermuda and the Bahamas by tomorrow, 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. Tropical storm conditions are expected on Bermuda beginning Friday night or early Saturday, and a Tropical Storm Warning is in effect for the island. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 25.0N 61.2W 125 KT 145 MPH 12H 01/1200Z 27.2N 61.8W 125 KT 145 MPH 24H 02/0000Z 30.2N 61.6W 115 KT 130 MPH 36H 02/1200Z 32.9N 60.5W 105 KT 120 MPH 48H 03/0000Z 35.0N 58.9W 95 KT 110 MPH 60H 03/1200Z 36.6N 56.8W 85 KT 100 MPH 72H 04/0000Z 38.7N 53.8W 80 KT 90 MPH 96H 05/0000Z 44.6N 47.2W 75 KT 85 MPH 120H 06/0000Z 48.9N 42.5W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin

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