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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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Summary for Hurricane Sam (AT3/AL182021)
2021-09-27 04:49:03| National Hurricane Center (Atlantic)
...HURRICANE HUNTER AIRCRAFT FINDS SAM HAS PEAKED IN INTENSITY... ...EXPECTED TO REMAIN A MAJOR HURRICANE FOR SEVERAL DAYS... As of 11:00 PM AST Sun Sep 26 the center of Sam was located near 14.7, -50.8 with movement NW at 7 mph. The minimum central pressure was 943 mb with maximum sustained winds of about 145 mph.
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Hurricane Sam Public Advisory Number 18
2021-09-27 04:49:03| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Sep 26 2021 000 WTNT33 KNHC 270248 TCPAT3 BULLETIN Hurricane Sam Advisory Number 18 NWS National Hurricane Center Miami FL AL182021 1100 PM AST Sun Sep 26 2021 ...HURRICANE HUNTER AIRCRAFT FINDS SAM HAS PEAKED IN INTENSITY... ...EXPECTED TO REMAIN A MAJOR HURRICANE FOR SEVERAL DAYS... SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION ----------------------------------------------- LOCATION...14.7N 50.8W ABOUT 850 MI...1365 KM ESE OF THE NORTHERN LEEWARD ISLANDS MAXIMUM SUSTAINED WINDS...145 MPH...230 KM/H PRESENT MOVEMENT...NW OR 315 DEGREES AT 7 MPH...11 KM/H MINIMUM CENTRAL PRESSURE...943 MB...27.85 INCHES WATCHES AND WARNINGS -------------------- There are no coastal watches or warnings in effect. DISCUSSION AND OUTLOOK ---------------------- At 1100 PM AST (0300 UTC), the center of Hurricane Sam was located by a NOAA Hurricane Hunter aircraft near latitude 14.7 North, longitude 50.8 West. Sam is moving toward the northwest near 7 mph (11 km/h), and this motion is expected to continue for the next few days, along with a gradual increase in forward speed beginning around midweek. Data from the reconnaissance aircraft indicate that maximum sustained winds are near 145 mph (230 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 day or so. Thereafter, slow weakening is forecast. However, Sam is still expected to remain a major hurricane through midweek. Sam remains a small tropical cyclone. Hurricane-force winds extend outward up to 30 miles (45 km) from the center and tropical-storm-force winds extend outward up to 90 miles (150 km). The estimated minimum central pressure based on recent reports from the aircraft is 943 mb (27.85 inches). HAZARDS AFFECTING LAND ---------------------- SURF: Swells generated by Sam are forecast to reach the Lesser Antilles early this week. 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 AM AST. $$ Forecaster Stewart
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Hurricane Sam Wind Speed Probabilities Number 18
2021-09-27 04:49:03| National Hurricane Center (Atlantic)
Issued at 0300 UTC MON SEP 27 2021 000 FONT13 KNHC 270248 PWSAT3 HURRICANE SAM WIND SPEED PROBABILITIES NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182021 0300 UTC MON SEP 27 2021 AT 0300Z THE CENTER OF HURRICANE SAM WAS LOCATED NEAR LATITUDE 14.7 NORTH...LONGITUDE 50.8 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 125 KTS...145 MPH...230 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 00Z 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 00Z MON 12Z MON 00Z TUE 12Z TUE 00Z WED 00Z THU 00Z FRI PERIODS TO TO TO TO TO TO TO 12Z MON 00Z TUE 12Z TUE 00Z WED 00Z THU 00Z FRI 00Z SAT FORECAST HOUR (12) (24) (36) (48) (72) (96) (120) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - LOCATION KT BERMUDA 34 X X( X) X( X) X( X) X( X) X( X) 19(19) BERMUDA 50 X X( X) X( X) X( X) X( X) X( X) 8( 8) BERMUDA 64 X X( X) X( X) X( X) X( X) X( X) 4( 4) SAINT THOMAS 34 X X( X) X( X) X( X) X( X) 3( 3) X( 3) SAINT MAARTEN 34 X X( X) X( X) X( X) 2( 2) 5( 7) X( 7) SABA 34 X X( X) X( X) X( X) 1( 1) 4( 5) X( 5) ST EUSTATIUS 34 X X( X) X( X) X( X) 2( 2) 3( 5) X( 5) ST KITTS-NEVIS 34 X X( X) X( X) X( X) 2( 2) 3( 5) X( 5) BARBUDA 34 X X( X) X( X) X( X) 4( 4) 5( 9) 1(10) ANTIGUA 34 X X( X) X( X) X( X) 4( 4) 3( 7) 1( 8) GUADELOUPE 34 X X( X) X( X) X( X) 3( 3) 2( 5) X( 5) DOMINICA 34 X X( X) X( X) X( X) 2( 2) X( 2) 1( 3) $$ FORECASTER STEWART
Hurricane Sam Forecast Advisory Number 18
2021-09-27 04:48:33| National Hurricane Center (Atlantic)
Issued at 0300 UTC MON SEP 27 2021 000 WTNT23 KNHC 270248 TCMAT3 HURRICANE SAM FORECAST/ADVISORY NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182021 0300 UTC MON SEP 27 2021 THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT. HURRICANE CENTER LOCATED NEAR 14.7N 50.8W AT 27/0300Z POSITION ACCURATE WITHIN 15 NM PRESENT MOVEMENT TOWARD THE NORTHWEST OR 315 DEGREES AT 6 KT ESTIMATED MINIMUM CENTRAL PRESSURE 943 MB EYE DIAMETER 15 NM MAX SUSTAINED WINDS 125 KT WITH GUSTS TO 150 KT. 64 KT....... 25NE 20SE 20SW 20NW. 50 KT....... 40NE 30SE 25SW 30NW. 34 KT....... 80NE 80SE 60SW 70NW. 12 FT SEAS..120NE 75SE 90SW 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 14.7N 50.8W AT 27/0300Z AT 27/0000Z CENTER WAS LOCATED NEAR 14.5N 50.6W FORECAST VALID 27/1200Z 15.3N 51.6W MAX WIND 125 KT...GUSTS 150 KT. 64 KT... 25NE 20SE 20SW 20NW. 50 KT... 40NE 30SE 25SW 30NW. 34 KT... 90NE 80SE 60SW 70NW. FORECAST VALID 28/0000Z 16.2N 52.8W MAX WIND 120 KT...GUSTS 145 KT. 64 KT... 25NE 20SE 20SW 20NW. 50 KT... 50NE 40SE 30SW 40NW. 34 KT... 90NE 80SE 60SW 70NW. FORECAST VALID 28/1200Z 17.0N 53.9W MAX WIND 120 KT...GUSTS 145 KT. 64 KT... 30NE 25SE 20SW 25NW. 50 KT... 50NE 40SE 30SW 40NW. 34 KT... 90NE 80SE 60SW 80NW. FORECAST VALID 29/0000Z 17.8N 55.0W MAX WIND 120 KT...GUSTS 145 KT. 64 KT... 35NE 30SE 25SW 30NW. 50 KT... 50NE 45SE 35SW 40NW. 34 KT... 90NE 80SE 70SW 80NW. FORECAST VALID 29/1200Z 18.7N 56.3W MAX WIND 115 KT...GUSTS 140 KT. 50 KT... 50NE 50SE 40SW 40NW. 34 KT...100NE 90SE 70SW 80NW. FORECAST VALID 30/0000Z 20.0N 58.0W MAX WIND 115 KT...GUSTS 140 KT. 50 KT... 60NE 50SE 45SW 45NW. 34 KT...110NE 90SE 70SW 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 01/0000Z 23.4N 61.0W MAX WIND 110 KT...GUSTS 135 KT. OUTLOOK VALID 02/0000Z 28.4N 62.6W MAX WIND 105 KT...GUSTS 130 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 14.7N 50.8W NEXT ADVISORY AT 27/0900Z $$ FORECASTER STEWART
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