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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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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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Tropical Depression Twenty Forecast Discussion Number 1
2021-09-29 16:36:42| National Hurricane Center (Atlantic)
Issued at 200 PM CVT Wed Sep 29 2021 000 WTNT45 KNHC 291436 TCDAT5 Tropical Depression Twenty Discussion Number 1 NWS National Hurricane Center Miami FL AL202021 200 PM CVT Wed Sep 29 2021 The area of low pressure located over the far eastern tropical Atlantic that NHC has been monitoring has now become a tropical depression, the twentieth tropical cyclone of the 2021 Atlantic hurricane season. Satellite images indicate that the system is producing a large area of showers and thunderstorms that have become fairly well organized around the center. An ASCAT-A pass from a few hours ago indicated that the system now has a well-defined circulation and that the radius of maximum wind is 30-40 n mi north of the center. The initial intensity is set at 30 kt based on the ASCAT data and the T2.0/30 kt Dvorak classifications from TAFB and SAB. The minimum pressure of 1007 mb is partially based on data from a ship report that passed near the depression. Based on satellite fixes, the depression appears to be moving west-northwestward at about 12 kt. The system is currently located on the south side of a deep-layer ridge, and that feature should keep the cyclone on a west-northwest track during the next couple of days. After that time, the models show a mid- to upper-level low developing over the central tropical Atlantic, which erodes the western portion of the ridge. This change in the steering flow should cause the system to turn northwestward on Friday and then northward toward the end of the forecast period. Although the models generally agree on the evolution of the large-scale pattern, there are notable differences in the details, which leads to a fair amount of spread concerning when and where the turn to the north occurs. The GFS is farthest east while the ECMWF shows the westernmost solution. The NHC track forecast lies between those models and is near the TVCA multi-model consensus. The depression is expected to remain in conducive environmental conditions for strengthening during the next 2 or 3 days. During that time period, the storm is forecast to move over 28-29 deg C waters while embedded within an airmass of high mid-level moisture and very low wind shear (less than 10 kt). Therefore, steady strengthening seems likely, and the NHC forecast brings the system to a tropical storm by tonight and a hurricane in a couple of days. Beyond a few days, however, the models show a pronounced increase in southwesterly shear and a notably drier atmosphere. These unfavorable conditions should end the opportunity for strengthening and promote a weakening trend. The NHC intensity forecast is a near a blend of the HCCA, IVCN, and IVDR consensus models. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 8.3N 24.6W 30 KT 35 MPH 12H 30/0000Z 8.8N 25.8W 35 KT 40 MPH 24H 30/1200Z 9.5N 27.6W 45 KT 50 MPH 36H 01/0000Z 10.3N 29.9W 55 KT 65 MPH 48H 01/1200Z 11.2N 31.9W 65 KT 75 MPH 60H 02/0000Z 12.4N 33.7W 70 KT 80 MPH 72H 02/1200Z 14.0N 35.4W 70 KT 80 MPH 96H 03/1200Z 18.4N 38.8W 55 KT 65 MPH 120H 04/1200Z 24.3N 40.9W 45 KT 50 MPH $$ Forecaster Cangialosi
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Tropical Depression Twenty Forecast Advisory Number 1
2021-09-29 16:35:13| National Hurricane Center (Atlantic)
Issued at 1500 UTC WED SEP 29 2021 000 WTNT25 KNHC 291435 TCMAT5 TROPICAL DEPRESSION TWENTY FORECAST/ADVISORY NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL202021 1500 UTC WED SEP 29 2021 THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT. TROPICAL DEPRESSION CENTER LOCATED NEAR 8.3N 24.6W AT 29/1500Z POSITION ACCURATE WITHIN 30 NM PRESENT MOVEMENT TOWARD THE WEST-NORTHWEST OR 290 DEGREES AT 12 KT ESTIMATED MINIMUM CENTRAL PRESSURE 1007 MB MAX SUSTAINED WINDS 30 KT WITH GUSTS TO 40 KT. WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT. REPEAT...CENTER LOCATED NEAR 8.3N 24.6W AT 29/1500Z AT 29/1200Z CENTER WAS LOCATED NEAR 8.1N 24.2W FORECAST VALID 30/0000Z 8.8N 25.8W MAX WIND 35 KT...GUSTS 45 KT. 34 KT... 60NE 0SE 0SW 50NW. FORECAST VALID 30/1200Z 9.5N 27.6W MAX WIND 45 KT...GUSTS 55 KT. 34 KT... 80NE 80SE 40SW 70NW. FORECAST VALID 01/0000Z 10.3N 29.9W MAX WIND 55 KT...GUSTS 65 KT. 50 KT... 30NE 20SE 0SW 30NW. 34 KT... 90NE 90SE 40SW 70NW. FORECAST VALID 01/1200Z 11.2N 31.9W MAX WIND 65 KT...GUSTS 80 KT. 64 KT... 20NE 0SE 0SW 0NW. 50 KT... 40NE 30SE 0SW 30NW. 34 KT...100NE 100SE 40SW 70NW. FORECAST VALID 02/0000Z 12.4N 33.7W MAX WIND 70 KT...GUSTS 85 KT. 50 KT... 40NE 40SE 20SW 30NW. 34 KT...110NE 100SE 40SW 90NW. FORECAST VALID 02/1200Z 14.0N 35.4W MAX WIND 70 KT...GUSTS 85 KT. 50 KT... 40NE 40SE 20SW 30NW. 34 KT...110NE 100SE 40SW 90NW. EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 150 NM ON DAY 4 AND 175 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY OUTLOOK VALID 03/1200Z 18.4N 38.8W MAX WIND 55 KT...GUSTS 65 KT. OUTLOOK VALID 04/1200Z 24.3N 40.9W MAX WIND 45 KT...GUSTS 55 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 8.3N 24.6W NEXT ADVISORY AT 29/2100Z $$ FORECASTER CANGIALOSI
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Hurricane Sam Forecast Discussion Number 27
2021-09-29 10:38:37| National Hurricane Center (Atlantic)
Issued at 500 AM AST Wed Sep 29 2021 000 WTNT43 KNHC 290838 TCDAT3 Hurricane Sam Discussion Number 27 NWS National Hurricane Center Miami FL AL182021 500 AM AST Wed Sep 29 2021 The eye of Sam has become cloud filled in infrared satellite imagery overnight, but the ring of deep convection surrounding the eye has cooled. There appears to be a southwest-to-northeast tilt to Sam's circulation as some modest southwesterly shear seems to be impinging on the hurricane. An Air Force Reserve Hurricane Hunter aircraft that has been investigating Sam overnight shows that the hurricane continues to fluctuate in intensity. The aircraft has reported a peak flight-level wind of 124 kt and SFMR winds of 108 kt. Therefore the initial wind speed has been set at 115 kt, which leans toward the higher flight-level-to-surface wind reduction. The aircraft also reported a minimum pressure of 950 mb, which is up a few millibars from the flight yesterday afternoon. The fluctuations in intensity that Sam has experienced over the past couple of days are fairly typical for hurricanes of this strength. As mentioned in the previous advisory, Sam will be moving into a lower vertical wind shear environment, and the expected faster forward speed decreases the potential for upwelling beneath the storm. As a result, some re-intensification is forecast, but difficult-to-predict eyewall replacement cycles could cause additional fluctuations in intensity over the next day or two. After 60 to 72 hours, a more pronounced weakening trend is likely to begin as the storm moves over cooler SSTs and the vertical shear increases. The global models indicate that Sam will begin its transition into a powerful extratropical cyclone late in the period, but that transition will likely not be completed until after 120 h. Sam is moving northwestward at about 8 kt. The track guidance remains in excellent agreement through 96 hours as Sam should move northwestward and then northward around the western portion of the subtropical ridge over the eastern Atlantic during the next few days. By Saturday, Sam is forecast to turn northeastward between the aforementioned ridge and a deep-layer trough over the northeastern U.S. and Nova Scotia. By late in the period, there is an increase in spread in the guidance which is related to how Sam interacts with the deep-layer trough. For now, the NHC track forecast at days 4 and 5 lies between the TVCA multi-model consensus and the HFIP corrected consensus aid. Overall, little change to the previous NHC track forecast was required for this advisory. 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 29/0900Z 18.9N 56.2W 115 KT 130 MPH 12H 29/1800Z 19.7N 57.3W 120 KT 140 MPH 24H 30/0600Z 21.0N 58.9W 120 KT 140 MPH 36H 30/1800Z 22.8N 60.4W 120 KT 140 MPH 48H 01/0600Z 25.2N 61.5W 115 KT 130 MPH 60H 01/1800Z 27.9N 62.0W 115 KT 130 MPH 72H 02/0600Z 30.8N 61.5W 110 KT 125 MPH 96H 03/0600Z 35.8N 57.5W 95 KT 110 MPH 120H 04/0600Z 40.8N 52.0W 80 KT 90 MPH $$ Forecaster Brown
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