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Hurricane Sam Forecast Discussion Number 11
2021-09-25 10:31:24| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Sep 25 2021 000 WTNT43 KNHC 250831 TCDAT3 Hurricane Sam Discussion Number 11 NWS National Hurricane Center Miami FL AL182021 500 AM AST Sat Sep 25 2021 Sam continues to rapidly intensify. Geostationary satellite and microwave images show that the storm has a very small and distinct eye surrounded by a nearly symmetric ring of cold cloud tops. The latest Dvorak estimates range from 90 to 102 kt, and based on that data, the initial intensity is increased to 95 kt. Although Sam is nearly a major hurricane, it remains quite compact with tropical-storm-force and hurricane-force winds estimated to only extend 50 n mi and 15 n mi from the center, respectively. The hurricane is moving west-northwestward at 11 kt and is currently being steered by a mid-level ridge to its north. There has been little change to the track forecast philosophy or model guidance. Sam is expected to continue west-northwestward during the next two or three days, but it is forecast to move at a notably slower pace of 6-8 kt during most of that time period. After that time, the ridge is expected to shift eastward as a deep-layer trough becomes established over the western Atlantic. This change in the steering pattern should cause Sam to turn northwestward and speed up some by the middle of next week. The models are in fairly good agreement, and the NHC track forecast is largely an update of the previous one. Based on this forecast, and nearly all of the reliable guidance, Sam is expected to still be well to the east or northeast of the northern Leeward Islands through day 5. Continued steady or rapid strengthening is expected during the next day or two as the hurricane remains in near ideal conditions of very low wind shear and warm 29 deg C waters. However, beyond that time the shear is expected to increase a little, and that will likely cause Sam to level off in strength or weaken slightly next week. The NHC intensity forecast is slightly above the models in the short term, given the impressive structure of the hurricane and favorable conditions, but falls in line with the consensus aids at the longer lead times. Regardless of how strong Sam gets, nearly all of the models indicate that it will remain a powerful hurricane during the next several days. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 12.8N 46.7W 95 KT 110 MPH 12H 25/1800Z 13.1N 48.0W 110 KT 125 MPH 24H 26/0600Z 13.5N 49.3W 115 KT 130 MPH 36H 26/1800Z 14.0N 50.4W 120 KT 140 MPH 48H 27/0600Z 14.7N 51.5W 120 KT 140 MPH 60H 27/1800Z 15.4N 52.5W 115 KT 130 MPH 72H 28/0600Z 16.3N 53.7W 115 KT 130 MPH 96H 29/0600Z 18.0N 56.0W 110 KT 125 MPH 120H 30/0600Z 20.1N 59.0W 110 KT 125 MPH $$ Forecaster Cangialosi
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Hurricane Sam Graphics
2021-09-25 04:36:06| National Hurricane Center (Atlantic)
5-Day Uncertainty Track last updated Sat, 25 Sep 2021 02:36:06 GMT Wind Speed Probabilities last updated Sat, 25 Sep 2021 02:36:06 GMT
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Hurricane Sam Forecast Discussion Number 10
2021-09-25 04:34:49| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Sep 24 2021 444 WTNT43 KNHC 250234 TCDAT3 Hurricane Sam Discussion Number 10 NWS National Hurricane Center Miami FL AL182021 1100 PM AST Fri Sep 24 2021 Sam developed a 10-n mi wide eye in infrared satellite images a few hours ago, surrounded by a ring of cloud tops as cold as about -70 degrees Celsius. The core of the hurricane remains compact. In fact, recent Synthetic Aperture Radar (SAR) data indicated that the radius of maximum winds is only about 6 n mi. Dvorak estimates were T5.0/90 kt from TAFB and T4.5/77 kt from SAB at 0000 UTC, and given the additional clearing of the eye since then, Sam's intensity is raised to 85 kt. Sam has been moving toward the west-northwest during the past 6 to 12 hours with a motion of 285/12 kt. The track forecast reasoning remains the same, and the model guidance is packed more tightly than normal through day 5. A blocking ridge lying to the north and northwest is expected to cause Sam to slow down over the weekend and maintain a motion toward the west or west-northwest. On days 3 through 5, the ridge is expected to shift eastward, with a deep-layer trough developing over the western Atlantic. This should allow Sam to turn northwestward toward the end of the forecast period. The NHC track forecast has not budged much and remains close to the TVCA consensus aid. Based on this forecast, and nearly all of the reliable guidance, Sam is expected to still be well to the east or northeast of the northern Leeward Islands through day 5. Deep-layer shear is expected to be less than 10 kt for the next day or two, and Sam will be heading toward waters of higher oceanic heat content. These conditions favor continued strengthening, and the hurricane is forecast to become a major hurricane on Saturday and possibly reach a peak intensity in 2 to 3 days. For this period, the NHC forecast is close to the HCCA consensus aid and is near the high end of the guidance envelope. As is usually the case with hurricanes this small and strong, fluctuations in intensity due to eyewall replacement cycles will be possible. On days 3 through 5, some increase in shear as Sam approaches the deep-layer western Atlantic trough is possible, and modest weakening is shown at those times. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 12.4N 45.9W 85 KT 100 MPH 12H 25/1200Z 12.7N 47.4W 100 KT 115 MPH 24H 26/0000Z 13.1N 48.8W 110 KT 125 MPH 36H 26/1200Z 13.5N 50.0W 115 KT 130 MPH 48H 27/0000Z 14.1N 51.2W 120 KT 140 MPH 60H 27/1200Z 14.8N 52.4W 120 KT 140 MPH 72H 28/0000Z 15.7N 53.5W 115 KT 130 MPH 96H 29/0000Z 17.4N 55.8W 110 KT 125 MPH 120H 30/0000Z 19.5N 58.8W 110 KT 125 MPH $$ Forecaster Berg
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Summary for Hurricane Sam (AT3/AL182021)
2021-09-25 04:34:20| National Hurricane Center (Atlantic)
...SAM NOW A CATEGORY 2 HURRICANE... ...FORECAST TO BECOME A MAJOR HURRICANE ON SATURDAY... As of 11:00 PM AST Fri Sep 24 the center of Sam was located near 12.4, -45.9 with movement WNW at 14 mph. The minimum central pressure was 982 mb with maximum sustained winds of about 100 mph.
Hurricane Sam Wind Speed Probabilities Number 10
2021-09-25 04:34:20| National Hurricane Center (Atlantic)
Issued at 0300 UTC SAT SEP 25 2021 000 FONT13 KNHC 250234 PWSAT3 HURRICANE SAM WIND SPEED PROBABILITIES NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182021 0300 UTC SAT SEP 25 2021 AT 0300Z THE CENTER OF HURRICANE SAM WAS LOCATED NEAR LATITUDE 12.4 NORTH...LONGITUDE 45.9 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 85 KTS ...100 MPH...155 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 SAT 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 SAT 12Z SAT 00Z SUN 12Z SUN 00Z MON 00Z TUE 00Z WED PERIODS TO TO TO TO TO TO TO 12Z SAT 00Z SUN 12Z SUN 00Z MON 00Z TUE 00Z WED 00Z THU FORECAST HOUR (12) (24) (36) (48) (72) (96) (120) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - LOCATION KT VIEQUES PR 34 X X( X) X( X) X( X) X( X) X( X) 3( 3) SAINT THOMAS 34 X X( X) X( X) X( X) X( X) X( X) 5( 5) SAINT CROIX 34 X X( X) X( X) X( X) X( X) X( X) 4( 4) SAINT MAARTEN 34 X X( X) X( X) X( X) X( X) 1( 1) 10(11) SAINT MAARTEN 50 X X( X) X( X) X( X) X( X) X( X) 3( 3) SAINT MAARTEN 64 X X( X) X( X) X( X) X( X) X( X) 2( 2) SABA 34 X X( X) X( X) X( X) X( X) 1( 1) 8( 9) SABA 50 X X( X) X( X) X( X) X( X) X( X) 3( 3) SABA 64 X X( X) X( X) X( X) X( X) X( X) 1( 1) ST EUSTATIUS 34 X X( X) X( X) X( X) X( X) 1( 1) 8( 9) ST EUSTATIUS 50 X X( X) X( X) X( X) X( X) X( X) 3( 3) ST EUSTATIUS 64 X X( X) X( X) X( X) X( X) X( X) 1( 1) ST KITTS-NEVIS 34 X X( X) X( X) X( X) X( X) 2( 2) 8(10) ST KITTS-NEVIS 50 X X( X) X( X) X( X) X( X) X( X) 3( 3) ST KITTS-NEVIS 64 X X( X) X( X) X( X) X( X) X( X) 2( 2) BARBUDA 34 X X( X) X( X) X( X) X( X) 3( 3) 13(16) BARBUDA 50 X X( X) X( X) X( X) X( X) 1( 1) 5( 6) BARBUDA 64 X X( X) X( X) X( X) X( X) X( X) 3( 3) ANTIGUA 34 X X( X) X( X) X( X) X( X) 3( 3) 10(13) ANTIGUA 50 X X( X) X( X) X( X) X( X) X( X) 5( 5) ANTIGUA 64 X X( X) X( X) X( X) X( X) X( X) 3( 3) GUADELOUPE 34 X X( X) X( X) X( X) X( X) 2( 2) 9(11) GUADELOUPE 50 X X( X) X( X) X( X) X( X) X( X) 3( 3) GUADELOUPE 64 X X( X) X( X) X( X) X( X) X( X) 2( 2) AVES 34 X X( X) X( X) X( X) X( X) X( X) 3( 3) DOMINICA 34 X X( X) X( X) X( X) X( X) 2( 2) 5( 7) MARTINIQUE 34 X X( X) X( X) X( X) X( X) 2( 2) 4( 6) SAINT LUCIA 34 X X( X) X( X) X( X) X( X) 2( 2) 2( 4) BARBADOS 34 X X( X) X( X) X( X) X( X) 3( 3) 2( 5) $$ FORECASTER BERG
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