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Hurricane Marie Forecast Discussion Number 21

2020-10-04 10:34:39| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sun Oct 04 2020 000 WTPZ43 KNHC 040834 TCDEP3 Hurricane Marie Discussion Number 21 NWS National Hurricane Center Miami FL EP182020 200 AM PDT Sun Oct 04 2020 The satellite presentation of Marie has continued to degrade overnight with a less symmetric cloud pattern, no signs of an eye, and perhaps some indication that the mid-level circulation is beginning to decouple from the low-level center. The initial intensity is reduced to 90 kt, consistent with the latest estimates from TAFB/SAB. Further rapid weakening is expected today as shear is forecast to increase while the hurricane moves over cooler waters. Marie should lose its deep convection around day 4 due to more cold water and higher shear, so remnant low status is forecast then. The new intensity forecast is similar to the last one, near or below the model consensus. The hurricane is still headed northwestward near 7 kt. The eastern Pacific subtropical ridge to the north should keep Marie moving generally west-northwestward or northwestward at about the same forward speed during the next few days. Near the end of the forecast period, Marie could turn more poleward due to an approaching mid-latitude trough. The model guidance is fairly divergent at long range, however, with some of the guidance showing the tropical cyclone being too shallow to feel the trough and continuing a northwest track, with others recurving ahead of the trough. The new forecast shows a north-northwest turn as a compromise, just a little west of the previous NHC prediction. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 20.1N 128.1W 90 KT 105 MPH 12H 04/1800Z 20.5N 129.0W 70 KT 80 MPH 24H 05/0600Z 21.1N 130.4W 60 KT 70 MPH 36H 05/1800Z 21.7N 131.7W 50 KT 60 MPH 48H 06/0600Z 22.4N 133.1W 40 KT 45 MPH 60H 06/1800Z 23.2N 134.5W 35 KT 40 MPH 72H 07/0600Z 24.0N 135.5W 30 KT 35 MPH 96H 08/0600Z 24.9N 136.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 09/0600Z 26.0N 137.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake

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Hurricane Marie Forecast Discussion Number 20

2020-10-04 04:33:38| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sat Oct 03 2020 000 WTPZ43 KNHC 040233 TCDEP3 Hurricane Marie Discussion Number 20 NWS National Hurricane Center Miami FL EP182020 800 PM PDT Sat Oct 03 2020 Marie crossed the 26 degree SST isotherm earlier this evening and the cold waters and accompanying dry,stable air are having a big impact on the storm. Recent microwave imagery shows that the hurricane no longer has an closed eyewall in the southern portion of its inner core. Furthermore, cloud top temperatures have warmed and the hurricane's eye is barely discernible. A blend of Final-T and CI Dvorak numbers from TAFB is the primary basis for the initial intensity of 100 kt. Continued rapid weakening is anticipated for the next 36 to 48 h as Marie encounters very hostile environmental conditions. After that time, continued weakening is likely and most of the dynamical models indicate that the cyclone will lose its convection by around day 5, if not a little sooner. The hurricane is moving northwestward near 7 kt. A ridge extending westward from southwestern U.S. should keep Marie moving generally west-northwestward or northwestward at about the same forward speed for the next several days. Near the end of the forecast period, Marie will likely turn northward ahead of a deep layer trough approaching from the northwest. The spread in the track guidance is quite low, and confidence in the track forecast is fairly high, particularly since almost no change was made to the previous advisory forecast. Both the track and intensity forecasts are based on the multi-model consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 19.5N 127.9W 100 KT 115 MPH 12H 04/1200Z 20.2N 128.8W 80 KT 90 MPH 24H 05/0000Z 20.9N 130.0W 65 KT 75 MPH 36H 05/1200Z 21.6N 131.3W 55 KT 65 MPH 48H 06/0000Z 22.3N 132.5W 45 KT 50 MPH 60H 06/1200Z 22.9N 133.8W 40 KT 45 MPH 72H 07/0000Z 23.7N 135.0W 35 KT 40 MPH 96H 08/0000Z 24.7N 136.0W 30 KT 35 MPH 120H 09/0000Z 26.0N 136.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky

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Hurricane Marie Forecast Discussion Number 19

2020-10-03 22:46:35| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sat Oct 03 2020 000 WTPZ43 KNHC 032046 TCDEP3 Hurricane Marie Discussion Number 19 NWS National Hurricane Center Miami FL EP182020 200 PM PDT Sat Oct 03 2020 Marie is finally beginning to show signs of weakening. Recent GOES-17 infrared satellite imagery indicates cloud tops are warming in the western eyewall, and water vapor imagery shows drier air impinging on the western periphery of the storm. Despite this, there is still deep convection with cloud tops colder than -70 degrees Celsius persisting in the eastern eyewall. The initial intensity is slightly lowered to 110 kt with this advisory based on a blend of TAFB and SAB Dvorak classifications and a 16 UTC SATCON estimate of 114 kt. Marie is likely beginning to experience increased deep-layer southwesterly wind shear as it moves toward the 26 degree Celsius sea surface temperature isotherm. With environmental conditions becoming increasingly hostile, Marie is expected to steadily, and perhaps rapidly, weaken over the next several days. Marie is forecast to weaken into a tropical storm within 36 hours, as the storm moves over cooler waters and into an environment with 30 kt of vertical wind shear. Steady weakening should continue through early next week, and the system is expected to become a tropical depression by Wednesday and a remnant low on Thursday. Now that the system is finally weakening, the latest NHC intensity forecast reflects a more rapid downward trend supported by the model consensus aids. Marie's initial motion is 325/8 kt, slightly more northwestward than the previous advisory. Marie should continue moving northwestward or west-northwestward for the next several days along the southwest periphery of a mid-level ridge centered over the southwestern United States. The latest model guidance remains tightly clustered during the first 2-3 days of the forecast. Then, the bulk of the guidance indicates Marie will slow down and turn more northward late next week ahead of a deep-layer trough to the north of the storm. Given this recurving scenario, there is more significant spread in the guidance at day 4 and beyond, with the GFS still farther to the right than most other models. Overall, the official NHC track forecast has been adjusted slightly right of the previous one in agreement with the TVCE/HCCA aids. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 19.1N 127.3W 110 KT 125 MPH 12H 04/0600Z 19.8N 128.1W 95 KT 110 MPH 24H 04/1800Z 20.6N 129.1W 75 KT 85 MPH 36H 05/0600Z 21.3N 130.4W 60 KT 70 MPH 48H 05/1800Z 21.9N 131.8W 50 KT 60 MPH 60H 06/0600Z 22.5N 133.0W 40 KT 45 MPH 72H 06/1800Z 23.0N 134.2W 35 KT 40 MPH 96H 07/1800Z 24.0N 135.5W 30 KT 35 MPH 120H 08/1800Z 25.5N 136.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Reinhart/Berg

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Tropical Storm Gamma Forecast Discussion Number 6

2020-10-03 22:38:08| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Sat Oct 03 2020 000 WTNT45 KNHC 032037 TCDAT5 Tropical Storm Gamma Discussion Number 6 NWS National Hurricane Center Miami FL AL252020 400 PM CDT Sat Oct 03 2020 Surface observations from the Yucatan Peninsula along with high-resolution visible satellite imagery indicated that the center of Gamma made landfall in the vicinity of Tulum, Mexico, shortly before 1700 UTC. Earlier aircraft observations and pressure measurements from Tulum showed that the system was very near hurricane strength when it made landfall. A ragged eye appeared in the visible images shortly after the center crossed the coast, but that feature has since become obscured. Since Gamma has likely been slowly weakening while moving over land, the current intensity has been set to 55 kt. Continued gradual weakening is likely into Sunday while the center either moves over land or interacts with nearby land. Some re-strengthening is expected to begin by Monday, but the numerical guidance is not very enthusiastic about intensification over the Gulf, probably due to the combination of drier air and the interaction with another low pressure system to the east. The official intensity forecast is not much different from the model consensus. Gamma has been moving northwestward, but it is expected to turn north-northwestward while moving near and into a weakness in the subtropical ridge over the next day or so. The global models predict that a trough to the north of the tropical cyclone will lift northeastward and bypass Gamma. In a couple of days, a ridge is forecast to build back, albeit weakly, across the Gulf of Mexico. This is expected to cause the system to turn westward to southwestward over the latter part of the forecast period. The more reliable global models show the system meandering over the southern Bay of Campeche in 4 to 5 days, and so does the official forecast. KEY MESSAGES: 1. Gamma is expected to produce heavy rainfall for several days over portions of southeastern Mexico, the Yucatan Peninsula, Central America, and far western Cuba. This rainfall could result in life-threatening flash flooding and mudslides, particularly in the mountainous regions of southeastern Mexico and Central America. 2. Even though Gamma has moved inland, tropical storm conditions will continue along the east coast of the Yucatan Peninsula through this evening and are expected to spread along the north coast within the Tropical Storm Warning area tonight and on Sunday. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 20.7N 87.7W 55 KT 65 MPH...INLAND 12H 04/0600Z 21.3N 88.0W 45 KT 50 MPH...INLAND 24H 04/1800Z 22.0N 88.2W 40 KT 45 MPH...OVER WATER 36H 05/0600Z 22.1N 88.4W 40 KT 45 MPH 48H 05/1800Z 22.0N 89.1W 45 KT 50 MPH 60H 06/0600Z 21.6N 90.4W 50 KT 60 MPH 72H 06/1800Z 21.0N 91.5W 50 KT 60 MPH 96H 07/1800Z 20.0N 92.0W 45 KT 50 MPH 120H 08/1800Z 20.0N 93.0W 40 KT 45 MPH $$ Forecaster Pasch

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Tropical Storm Gamma Forecast Discussion Number 5

2020-10-03 16:57:57| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Sat Oct 03 2020 000 WTNT45 KNHC 031457 TCDAT5 Tropical Storm Gamma Discussion Number 5 NWS National Hurricane Center Miami FL AL252020 1000 AM CDT Sat Oct 03 2020 Observations from both the Air Force and NOAA Hurricane Hunters indicate that Gamma has continued to strengthen this morning. The cloud pattern has continued to become better organized, with an eye trying to become evident on high-resolution satellite images from the GOES-16 mesoscale sectors. Flight-level and SFMR-observed surface winds from the aircraft support an intensity of 60 kt, and the storm could strengthen a little more as long as the center remains over water. Since Gamma will be near or at hurricane intensity when it makes landfall later today, the government of Mexico has issued a Hurricane Warning for a portion of the northeastern Yucatan Peninsula. Gamma should weaken some while it moves over land tonight. Some re-intensification is likely after the center moves into the southern Gulf of Mexico. However, the numerical guidance does not show much strengthening during the next few days, possibly due to the influence of drier air and/or the interaction with another area of low pressure to the east of Gamma. The official intensity forecast is near or above the model consensus. Gamma continues northwestward at near 8 kt. The cyclone is expected to turn north-northwestward and move through a break in the subtropical ridge through 36 hours or so. Thereafter, a trough to the north moves eastward, bypassing Gamma, and later in the forecast period a ridge builds weakly over the Gulf of Mexico. This should cause the cyclone to turn toward the west and southwest. The official track forecast is close to the multi-model consensus, TVCN. Although Gamma has strengthened, its biggest threat continues to be torrential rains, flooding, and mudslides especially near and over mountainous terrain. KEY MESSAGES: 1. Gamma is expected to produce heavy rainfall for several days over portions of southeastern Mexico, the Yucatan Peninsula, Central America, and far western Cuba. This rainfall could result in life-threatening flash flooding and mudslides, particularly in the mountainous regions of southeastern Mexico and Central America. 2. Gamma is very near hurricane strength and will be near or at hurricane intensity when the center moves inland over the Yucatan Peninsula later today. A Hurricane Warning is now in effect for portions of the east coast of the Yucatan Peninsula, where tropical storm conditions are already occurring. Tropical storm conditions are expected along the north coast of the Yucatan Peninsula within the Tropical Storm Warning area later today and on Sunday. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 20.0N 87.3W 60 KT 70 MPH 12H 04/0000Z 20.8N 87.8W 55 KT 65 MPH...INLAND 24H 04/1200Z 21.8N 88.1W 40 KT 45 MPH...OVER WATER 36H 05/0000Z 22.2N 88.3W 40 KT 45 MPH 48H 05/1200Z 22.3N 88.8W 45 KT 50 MPH 60H 06/0000Z 22.1N 89.7W 50 KT 60 MPH 72H 06/1200Z 22.0N 91.0W 50 KT 60 MPH 96H 07/1200Z 21.0N 92.5W 45 KT 50 MPH 120H 08/1200Z 20.0N 93.5W 40 KT 45 MPH $$ Forecaster Pasch

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