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Hurricane Sam Forecast Discussion Number 19
2021-09-27 10:49:06| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Sep 27 2021 000 WTNT43 KNHC 270848 TCDAT3 Hurricane Sam Discussion Number 19 NWS National Hurricane Center Miami FL AL182021 500 AM AST Mon Sep 27 2021 The satellite presentation of Sam deteriorated overnight, as GOES-16 infrared imagery showed periodic disruptions to Sam's inner core convection. The eye has not been readily apparent in conventional satellite imagery for much of the night, although very recent imagery suggests an eye could be re-emerging. Data from the reconnaissance aircraft last night indicated that an eyewall replacement cycle (ERC) was underway, and some dry mid-level air impinging on the western side of the circulation could also be negatively impacting Sam. No recent high-resolution microwave data is available, but an earlier scatterometer pass revealed that the tropical-storm-force wind radii had expanded just a bit in the eastern semicircle of the hurricane. The initial intensity is lowered to 115 kt for this advisory based on a blend of the objective and subjective Dvorak current intensity estimates. A NOAA hurricane hunter aircraft is scheduled to investigate Sam later this morning, which will provide crucial data to assess changes in Sam's structure and intensity. The initial motion is estimated to be northwestward, or 315/7 kt. A subtropical ridge to the north and northeast of Sam will remain the primary steering mechanism over the next several days, and Sam is expected to maintain a northwestward heading through midweek. Then, a mid- to upper-level trough is forecast to dig southward over the western Atlantic late this week. The deep-layer southerly flow ahead of this feature should cause Sam to move faster toward the north-northwest by 96 h, followed by a northward acceleration thereafter. The NHC forecast track is shifted slightly to the right of the previous one through the first 48-60 h of the forecast period, which accounts for the more northwestward initial motion observed during the past 12 h. Otherwise, the NHC track is virtually unchanged as the guidance has remained fairly consistent. Sam's intensity has likely peaked now that an ERC has commenced, but environmental conditions should allow Sam to persist as a major hurricane for the next several days. Sea-surface temperatures are expected to be 28 deg C or greater along Sam's track through 120 h, and the vertical wind shear is forecast to remain weak (< 10 kt) through at least midweek. Thus, the official NHC intensity forecast only shows very gradual weakening during the next several days, generally following the HCCA and IVCN consensus aids. Given the lower initial intensity of Sam, the latest NHC forecast is once again lower than the previous one. By 120 h, southerly shear associated with the deep-layer trough is forecast to increase over Sam, which should induce more weakening by this weekend. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 15.2N 51.4W 115 KT 130 MPH 12H 27/1800Z 15.9N 52.2W 115 KT 130 MPH 24H 28/0600Z 16.8N 53.3W 115 KT 130 MPH 36H 28/1800Z 17.7N 54.4W 115 KT 130 MPH 48H 29/0600Z 18.6N 55.6W 110 KT 125 MPH 60H 29/1800Z 19.6N 57.1W 110 KT 125 MPH 72H 30/0600Z 21.0N 58.8W 110 KT 125 MPH 96H 01/0600Z 24.9N 61.6W 110 KT 125 MPH 120H 02/0600Z 30.5N 62.0W 105 KT 120 MPH $$ Forecaster Reinhart
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Hurricane Sam Public Advisory Number 19
2021-09-27 10:45:35| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Sep 27 2021 000 WTNT33 KNHC 270845 TCPAT3 BULLETIN Hurricane Sam Advisory Number 19 NWS National Hurricane Center Miami FL AL182021 500 AM AST Mon Sep 27 2021 ...SAM EXPECTED TO REMAIN A MAJOR HURRICANE FOR SEVERAL DAYS... ...HURRICANE HUNTER AIRCRAFT TO INVESTIGATE SAM LATER TODAY... SUMMARY OF 500 AM AST...0900 UTC...INFORMATION ---------------------------------------------- LOCATION...15.2N 51.4W ABOUT 800 MI...1290 KM ESE OF THE NORTHERN LEEWARD ISLANDS MAXIMUM SUSTAINED WINDS...130 MPH...215 KM/H PRESENT MOVEMENT...NW OR 315 DEGREES AT 8 MPH...13 KM/H MINIMUM CENTRAL PRESSURE...952 MB...28.12 INCHES WATCHES AND WARNINGS -------------------- There are no coastal watches or warnings in effect. DISCUSSION AND OUTLOOK ---------------------- At 500 AM AST (0900 UTC), the center of Hurricane Sam was located near latitude 15.2 North, longitude 51.4 West. Sam is moving toward the northwest near 8 mph (13 km/h). This general motion is expected to continue for the next several days, with an increase in forward speed beginning on Thursday. 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. Little change in strength is expected during the next day or so. Thereafter, some slow weakening is forecast through midweek, although Sam should remain a major hurricane. Sam is a small hurricane. Hurricane-force winds extend outward up to 30 miles (45 km) from the center and tropical-storm-force winds extend outward up to 105 miles (165 km). The estimated minimum central pressure is 952 mb (28.12 inches). HAZARDS AFFECTING LAND ---------------------- SURF: Swells generated by Sam will reach the Lesser Antilles today and impact these islands for the next several days. 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 1100 AM AST. $$ Forecaster Reinhart
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Hurricane Sam Wind Speed Probabilities Number 19
2021-09-27 10:45:35| National Hurricane Center (Atlantic)
Issued at 0900 UTC MON SEP 27 2021 000 FONT13 KNHC 270845 PWSAT3 HURRICANE SAM WIND SPEED PROBABILITIES NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182021 0900 UTC MON SEP 27 2021 AT 0900Z THE CENTER OF HURRICANE SAM WAS LOCATED NEAR LATITUDE 15.2 NORTH...LONGITUDE 51.4 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 115 KTS...130 MPH...215 KM/H. Z INDICATES COORDINATED UNIVERSAL TIME (GREENWICH) ATLANTIC STANDARD TIME (AST)...SUBTRACT 4 HOURS FROM Z TIME EASTERN DAYLIGHT TIME (EDT)...SUBTRACT 4 HOURS FROM Z TIME CENTRAL DAYLIGHT TIME (CDT)...SUBTRACT 5 HOURS FROM Z TIME WIND SPEED PROBABILITY TABLE FOR SPECIFIC LOCATIONS CHANCES OF SUSTAINED (1-MINUTE AVERAGE) WIND SPEEDS OF AT LEAST ...34 KT (39 MPH... 63 KM/H)... ...50 KT (58 MPH... 93 KM/H)... ...64 KT (74 MPH...119 KM/H)... FOR LOCATIONS AND TIME PERIODS DURING THE NEXT 5 DAYS PROBABILITIES FOR LOCATIONS ARE GIVEN AS OP(CP) WHERE OP IS THE PROBABILITY OF THE EVENT BEGINNING DURING AN INDIVIDUAL TIME PERIOD (ONSET PROBABILITY) (CP) IS THE PROBABILITY OF THE EVENT OCCURRING BETWEEN 06Z MON AND THE FORECAST HOUR (CUMULATIVE PROBABILITY) PROBABILITIES ARE GIVEN IN PERCENT X INDICATES PROBABILITIES LESS THAN 1 PERCENT PROBABILITIES FOR 34 KT AND 50 KT ARE SHOWN AT A GIVEN LOCATION WHEN THE 5-DAY CUMULATIVE PROBABILITY IS AT LEAST 3 PERCENT. PROBABILITIES FOR 34...50...64 KT SHOWN WHEN THE 5-DAY 64-KT CUMULATIVE PROBABILITY IS AT LEAST 1 PERCENT. - - - - WIND SPEED PROBABILITIES FOR SELECTED LOCATIONS - - - - FROM FROM FROM FROM FROM FROM FROM TIME 06Z MON 18Z MON 06Z TUE 18Z TUE 06Z WED 06Z THU 06Z FRI PERIODS TO TO TO TO TO TO TO 18Z MON 06Z TUE 18Z TUE 06Z WED 06Z THU 06Z FRI 06Z SAT FORECAST HOUR (12) (24) (36) (48) (72) (96) (120) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - LOCATION KT BERMUDA 34 X X( X) X( X) X( X) X( X) 1( 1) 28(29) BERMUDA 50 X X( X) X( X) X( X) X( X) X( X) 10(10) BERMUDA 64 X X( X) X( X) X( X) X( X) X( X) 6( 6) SAINT THOMAS 34 X X( X) X( X) X( X) 1( 1) 2( 3) X( 3) SAINT MAARTEN 34 X X( X) X( X) X( X) 3( 3) 3( 6) X( 6) SABA 34 X X( X) X( X) X( X) 2( 2) 2( 4) X( 4) ST EUSTATIUS 34 X X( X) X( X) X( X) 2( 2) 2( 4) X( 4) ST KITTS-NEVIS 34 X X( X) X( X) X( X) 2( 2) 2( 4) X( 4) BARBUDA 34 X X( X) X( X) X( X) 5( 5) 3( 8) X( 8) ANTIGUA 34 X X( X) X( X) X( X) 4( 4) 1( 5) X( 5) GUADELOUPE 34 X X( X) X( X) X( X) 3( 3) X( 3) X( 3) $$ FORECASTER REINHART
Hurricane Sam Forecast Advisory Number 19
2021-09-27 10:44:35| National Hurricane Center (Atlantic)
Issued at 0900 UTC MON SEP 27 2021 000 WTNT23 KNHC 270844 TCMAT3 HURRICANE SAM FORECAST/ADVISORY NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182021 0900 UTC MON SEP 27 2021 THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT. HURRICANE CENTER LOCATED NEAR 15.2N 51.4W AT 27/0900Z POSITION ACCURATE WITHIN 20 NM PRESENT MOVEMENT TOWARD THE NORTHWEST OR 315 DEGREES AT 7 KT ESTIMATED MINIMUM CENTRAL PRESSURE 952 MB EYE DIAMETER 15 NM MAX SUSTAINED WINDS 115 KT WITH GUSTS TO 140 KT. 64 KT....... 25NE 20SE 20SW 20NW. 50 KT....... 40NE 30SE 30SW 35NW. 34 KT....... 90NE 90SE 60SW 70NW. 12 FT SEAS..120NE 90SE 120SW 120NW. 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 15.2N 51.4W AT 27/0900Z AT 27/0600Z CENTER WAS LOCATED NEAR 15.0N 51.1W FORECAST VALID 27/1800Z 15.9N 52.2W MAX WIND 115 KT...GUSTS 140 KT. 64 KT... 25NE 20SE 20SW 20NW. 50 KT... 40NE 30SE 30SW 35NW. 34 KT... 90NE 90SE 60SW 70NW. FORECAST VALID 28/0600Z 16.8N 53.3W MAX WIND 115 KT...GUSTS 140 KT. 64 KT... 30NE 25SE 20SW 25NW. 50 KT... 50NE 40SE 30SW 40NW. 34 KT... 90NE 90SE 60SW 80NW. FORECAST VALID 28/1800Z 17.7N 54.4W MAX WIND 115 KT...GUSTS 140 KT. 64 KT... 30NE 25SE 20SW 25NW. 50 KT... 50NE 40SE 30SW 40NW. 34 KT... 90NE 90SE 60SW 80NW. FORECAST VALID 29/0600Z 18.6N 55.6W MAX WIND 110 KT...GUSTS 135 KT. 64 KT... 35NE 30SE 25SW 30NW. 50 KT... 60NE 50SE 40SW 50NW. 34 KT...100NE 90SE 70SW 80NW. FORECAST VALID 29/1800Z 19.6N 57.1W MAX WIND 110 KT...GUSTS 135 KT. 50 KT... 60NE 50SE 40SW 50NW. 34 KT...110NE 100SE 70SW 80NW. FORECAST VALID 30/0600Z 21.0N 58.8W MAX WIND 110 KT...GUSTS 135 KT. 50 KT... 60NE 50SE 50SW 50NW. 34 KT...110NE 100SE 80SW 90NW. 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 01/0600Z 24.9N 61.6W MAX WIND 110 KT...GUSTS 135 KT. OUTLOOK VALID 02/0600Z 30.5N 62.0W MAX WIND 105 KT...GUSTS 130 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 15.2N 51.4W NEXT ADVISORY AT 27/1500Z $$ FORECASTER REINHART
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Hurricane Sam Forecast Discussion Number 18
2021-09-27 04:49:28| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Sep 26 2021 431 WTNT43 KNHC 270249 TCDAT3 Hurricane Sam Discussion Number 18 NWS National Hurricane Center Miami FL AL182021 1100 PM AST Sun Sep 26 2021 A NOAA Hurricane Hunter aircraft investigating Sam this afternoon and evening found that the major hurricane likely peaked in intensity at around 135 kt with a central pressure of about 929 mb between 1900-2200 UTC when the eye contracted down to about 7 nmi in diameter. Since that time, however, wind and radar data from the aircraft reveal that Sam has been undergoing an eyewall replacement cycle (ERC), including significant erosion of the eyewall convection in the eastern semicircle, which has resulted in the central pressure increasing by at least 14 mb in only a few hours. The eye diameter has also doubled in size now. The ERC is also confirmed by the ragged inner-core convection and cloud-filled eye that have developed in satellite imagery. The advisory intensity of 125 kt is based on a blend of the available reliable SFMR surface wind data and flight-level wind data, and also using the pressure-wind relationship for a 943-mb central pressure. The initial motion estimate is now 315/06 kt. A strong subtropical ridge to the north and northeast of Sam is forecast by the global and regional models to remain entrenched across the central and eastern Atlantic for the next several days, resulting in the hurricane moving northwestward for the 72 hours. Thereafter, a mid- to upper-level trough is forecast to dig southward just off the U.S. east coast, creating a deep southerly flow regime that will act to accelerate Sam northward on days 4 and 5. The new NHC track forecast is similar the previous advisory, and lies close to the tightly packed consensus models through 72 hours. In the 96-120 hour period, the models diverge significantly on when and where Sam will begin moving out toward the north, and the NHC track forecast favors the more eastward GFS solution since that model has been performing quite well with Sam thus far. Now that Sam is undergoing an ERC, fluctuations in intensity could occur for the next day or two while the vertical wind shear remains low at least than 10 kt. Thereafter, a slow weakening trend is expected due to a modest increase in the wind shear from the southwest and occasional intrusions of drier mid-level air. The NHC intensity forecast is a little lower than the previous advisory, mainly due to the lower initial intensity, and closely follows the HCCA and IVCN consensus model intensity forecasts. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 14.7N 50.8W 125 KT 145 MPH 12H 27/1200Z 15.3N 51.6W 125 KT 145 MPH 24H 28/0000Z 16.2N 52.8W 120 KT 140 MPH 36H 28/1200Z 17.0N 53.9W 120 KT 140 MPH 48H 29/0000Z 17.8N 55.0W 120 KT 140 MPH 60H 29/1200Z 18.7N 56.3W 115 KT 130 MPH 72H 30/0000Z 20.0N 58.0W 115 KT 130 MPH 96H 01/0000Z 23.4N 61.0W 110 KT 125 MPH 120H 02/0000Z 28.4N 62.6W 105 KT 120 MPH $$ Forecaster Stewart
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