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Hurricane Sam Forecast Discussion Number 28

2021-09-29 16:42:08| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Sep 29 2021 000 WTNT43 KNHC 291441 TCDAT3 Hurricane Sam Discussion Number 28 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Wed Sep 29 2021 Sam has a well-organized cloud pattern on satellite imagery, with a 90 n mi-wide Central Dense Overcast surrounded by numerous convective banding features. Upper-level outflow has now become better established to the southeast of the hurricane. A NOAA Hurricane Hunter mission from a couple of hours ago reported a 20 n mi-wide diameter circular eye. The current intensity is held at 115 kt for this advisory, which is a little higher than the maximum winds observed in the earlier aircraft mission. However, since the estimated minimum central pressure of 949 is a little lower than it was earlier this morning and Sam's intensity has been fluctuating, it is considered prudent not to lower the winds at this time. An Air Force Hurricane Hunter aircraft is scheduled to investigate the hurricane soon and will provide another intensity estimate. Sam continues its slow northwestward trek with the current motion remaining near 310/8 kt. Sam should move northwestward and then northward around the western portion of the subtropical ridge over the eastern Atlantic during the next few days, and turn toward the north-northeast and northeast later in the forecast period. The track guidance models are in very good agreement through 72 hours or so, with some increase in model spread thereafter. This increase in spread is largely due to how Sam will interact with a strong mid-latitude trough moving through Atlantic Canada. Some of the guidance suggests that this trough could partially bypass the hurricane around the end of the period and beyond, but this is not yet clear. The current NHC forecast track is not much different from the previous one and is in good agreement with the dynamical model consensus, TVCA. The hurricane will continue to move over warm waters and in an environment of low vertical shear and diffluent upper-level flow for the next 1-2 days. Thus, it would not be surprising to soon see some restrengthening. The official intensity forecast is essentially a blend of the latest Decay-SHIPS and LGEM predictions, and is very similar to the previous NHC forecast. Sam is likely to remain a major hurricane into this weekend. Key Messages: 1. Large swells generated by Sam are affecting the Leeward Islands and will spread to portions of the Virgin Islands, Puerto Rico, Hispaniola, the Bahamas, and Bermuda by Thursday or Friday. Significant swells will likely reach the east coast of the United States and Atlantic Canada by the weekend. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the advice of lifeguards and local officials through the upcoming weekend. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 19.4N 57.0W 115 KT 130 MPH 12H 30/0000Z 20.3N 58.1W 120 KT 140 MPH 24H 30/1200Z 21.8N 59.6W 120 KT 140 MPH 36H 01/0000Z 23.9N 61.0W 120 KT 140 MPH 48H 01/1200Z 26.6N 61.8W 115 KT 130 MPH 60H 02/0000Z 29.4N 61.8W 110 KT 125 MPH 72H 02/1200Z 32.0N 60.9W 105 KT 120 MPH 96H 03/1200Z 36.2N 57.3W 90 KT 105 MPH 120H 04/1200Z 39.5N 53.0W 75 KT 85 MPH $$ Forecaster Pasch

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Summary for Hurricane Sam (AT3/AL182021)

2021-09-29 16:41:52| National Hurricane Center (Atlantic)

...POWERFUL SAM CONTINUES MOVING SLOWLY NORTHWESTWARD... As of 11:00 AM AST Wed Sep 29 the center of Sam was located near 19.4, -57.0 with movement NW at 9 mph. The minimum central pressure was 949 mb with maximum sustained winds of about 130 mph.

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Hurricane Sam Public Advisory Number 28

2021-09-29 16:41:52| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Sep 29 2021 000 WTNT33 KNHC 291441 TCPAT3 BULLETIN Hurricane Sam Advisory Number 28 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Wed Sep 29 2021 ...POWERFUL SAM CONTINUES MOVING SLOWLY NORTHWESTWARD... SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION ----------------------------------------------- LOCATION...19.4N 57.0W ABOUT 405 MI...655 KM ENE OF THE NORTHERN LEEWARD ISLANDS MAXIMUM SUSTAINED WINDS...130 MPH...215 KM/H PRESENT MOVEMENT...NW OR 310 DEGREES AT 9 MPH...15 KM/H MINIMUM CENTRAL PRESSURE...949 MB...28.03 INCHES WATCHES AND WARNINGS -------------------- There are no coastal watches or warnings in effect. DISCUSSION AND OUTLOOK ---------------------- At 1100 AM AST (1500 UTC), the center of Hurricane Sam was located near latitude 19.4 North, longitude 57.0 West. Sam is moving toward the northwest near 9 mph (15 km/h), and this general motion with an increase in forward speed is expected during the next couple of days. A turn toward the north is forecast by Friday. On the forecast track, Sam will pass well to the east-northeast of the northern Leeward Islands through tonight. Maximum sustained winds are near 130 mph (215 km/h) with higher gusts. Sam is a category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Some fluctuations in intensity are expected during the next couple of days, but Sam is forecast to remain a major hurricane through late this week. Hurricane-force winds extend outward up to 40 miles (65 km) from the center and tropical-storm-force winds extend outward up to 125 miles (205 km). The minimum central pressure estimated from NOAA Hurricane Hunter aircraft observations is 949 mb (28.03 inches). HAZARDS AFFECTING LAND ---------------------- Key messages for Sam can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT3 and WMO header WTNT43 KNHC. SURF: 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. NEXT ADVISORY ------------- Next complete advisory at 500 PM AST. $$ Forecaster Pasch

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Hurricane Sam Forecast Advisory Number 28

2021-09-29 16:41:48| National Hurricane Center (Atlantic)

Issued at 1500 UTC WED SEP 29 2021 000 WTNT23 KNHC 291441 TCMAT3 HURRICANE SAM FORECAST/ADVISORY NUMBER 28 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182021 1500 UTC WED SEP 29 2021 THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT. HURRICANE CENTER LOCATED NEAR 19.4N 57.0W AT 29/1500Z POSITION ACCURATE WITHIN 15 NM PRESENT MOVEMENT TOWARD THE NORTHWEST OR 310 DEGREES AT 8 KT ESTIMATED MINIMUM CENTRAL PRESSURE 949 MB EYE DIAMETER 20 NM MAX SUSTAINED WINDS 115 KT WITH GUSTS TO 140 KT. 64 KT....... 35NE 30SE 25SW 30NW. 50 KT....... 60NE 50SE 40SW 50NW. 34 KT.......110NE 100SE 80SW 90NW. 12 FT SEAS..180NE 105SE 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 19.4N 57.0W AT 29/1500Z AT 29/1200Z CENTER WAS LOCATED NEAR 19.1N 56.6W FORECAST VALID 30/0000Z 20.3N 58.1W MAX WIND 120 KT...GUSTS 145 KT. 64 KT... 35NE 30SE 25SW 30NW. 50 KT... 60NE 50SE 40SW 50NW. 34 KT...120NE 110SE 90SW 100NW. FORECAST VALID 30/1200Z 21.8N 59.6W MAX WIND 120 KT...GUSTS 145 KT. 64 KT... 35NE 30SE 25SW 30NW. 50 KT... 60NE 50SE 40SW 50NW. 34 KT...120NE 110SE 90SW 100NW. FORECAST VALID 01/0000Z 23.9N 61.0W MAX WIND 120 KT...GUSTS 145 KT. 64 KT... 40NE 40SE 30SW 40NW. 50 KT... 70NE 60SE 50SW 60NW. 34 KT...120NE 120SE 90SW 100NW. FORECAST VALID 01/1200Z 26.6N 61.8W MAX WIND 115 KT...GUSTS 140 KT. 64 KT... 50NE 40SE 30SW 40NW. 50 KT... 70NE 70SE 50SW 60NW. 34 KT...130NE 140SE 90SW 100NW. FORECAST VALID 02/0000Z 29.4N 61.8W MAX WIND 110 KT...GUSTS 135 KT. 50 KT... 70NE 70SE 60SW 60NW. 34 KT...140NE 140SE 100SW 110NW. FORECAST VALID 02/1200Z 32.0N 60.9W MAX WIND 105 KT...GUSTS 130 KT. 50 KT... 70NE 70SE 60SW 60NW. 34 KT...150NE 150SE 120SW 130NW. 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 03/1200Z 36.2N 57.3W MAX WIND 90 KT...GUSTS 110 KT. OUTLOOK VALID 04/1200Z 39.5N 53.0W MAX WIND 75 KT...GUSTS 90 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 19.4N 57.0W NEXT ADVISORY AT 29/2100Z $$ FORECASTER PASCH

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