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Hurricane Marie Forecast Discussion Number 18

2020-10-03 16:38:55| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sat Oct 03 2020 000 WTPZ43 KNHC 031438 TCDEP3 Hurricane Marie Discussion Number 18 NWS National Hurricane Center Miami FL EP182020 800 AM PDT Sat Oct 03 2020 Marie shows little signs of weakening this morning as its satellite presentation remains impressive. A closed ring of eyewall convection with cloud top temperatures colder than -65 degrees C surrounds a well-defined 20 nm eye. The initial intensity is maintained at 115 kt based on a T6.0 Dvorak classification from SAB, which is supported by the latest ADT estimates. Marie is approaching an environment of increasing deep-layer southwesterly shear and SSTs below 26 degrees Celsius, which should induce weakening beginning later today that will continue through early next week. The latest SHIPS guidance indicates the vertical wind shear will strengthen to 30 kt by Mon and continue increasing through the end of the 5-day forecast period. Therefore, Marie is forecast to weaken to a tropical storm by early Monday and a tropical depression by the middle of next week. The NHC intensity forecast is held a bit higher than the model consensus through the first 12-24 hours of the forecast, since Marie has yet to show signs of weakening. As the environmental conditions become increasingly hostile, the official forecast shows more rapid weakening in line with the consensus intensity guidance. By day 5, simulated satellite imagery suggests the system will be a remnant low devoid of deep convection. Marie's initial motion is 310/8 kt, and the system is expected to generally continue moving northwestward for the next several days along the southwest periphery of a mid-level ridge. A deep-layer trough is expected to dig north of Marie during the middle of next week, which should begin turning the system more northward toward the end of the 5-day forecast period. A larger spread in the guidance is noted at days 4-5, as it remains somewhat unclear how much the trough will influence the weakening system based on timing differences between the GFS and ECMWF models. Overall, the NHC track forecast remains fairly close to the previous one, with slight changes based on the consensus aids including TVCE and HCCA. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 18.4N 126.9W 115 KT 130 MPH 12H 04/0000Z 19.1N 127.7W 105 KT 120 MPH 24H 04/1200Z 20.0N 128.7W 90 KT 105 MPH 36H 05/0000Z 20.6N 129.8W 70 KT 80 MPH 48H 05/1200Z 21.2N 131.2W 55 KT 65 MPH 60H 06/0000Z 21.9N 132.4W 45 KT 50 MPH 72H 06/1200Z 22.5N 133.7W 40 KT 45 MPH 96H 07/1200Z 23.5N 135.5W 30 KT 35 MPH 120H 08/1200Z 24.5N 136.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Reinhart/Berg

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Tropical Storm Gamma Forecast Discussion Number 4

2020-10-03 11:05:23| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Sat Oct 03 2020 000 WTNT45 KNHC 030905 TCDAT5 Tropical Storm Gamma Discussion Number 4 NWS National Hurricane Center Miami FL AL252020 400 AM CDT Sat Oct 03 2020 Satellite imagery and reports from an Air Force Reserve Hurricane Hunter aircraft indicate that Gamma is strengthening. A central dense overcast with cloud tops to -85C has formed, along with an outer convective band in the eastern semicircle. The aircraft has reported maximum 850 mb flight-level winds of 58 kt and reliable- looking surface wind estimates from the Stepped Frequency Microwave Radiometer of 40-45 kt. Based on this, the initial intensity is increased to 45 kt. The initial motion is again a little to the left of the previous advisory, 305/8 kt. During the next 24-36 h, Gamma is expected to turn northward as it tries to recurve into a break in the subtropical ridge caused by a mid-latitude trough over the eastern United States. The track guidance, however, is in good agreement that the trough will bypass the tropical cyclone, with a ridge building to the north after 36 h. This should cause Gamma to turn westward or southwestward between the ridge and the Central American cyclonic gyre to the south. There is uncertainty as to whether Gamma will move over the Gulf of Mexico before this turn occurs, as the ECMWF keeps the center inland or very near the coast. The new forecast track is north of the ECMWF, but a little to the south of the previous track. The foreast track calls for landfall on the northeastern Yucatan Peninsula in about 12 h, followed by the center reaching the Gulf of Mexico in about 36 h and a track near the coast of the Yucatan Peninsula thereafter. Conditions appear favorable for strengthening until landfall, and the forecast 12-h intensity of 50 kt could be conservative given current trends. The remainder of the intensity forecast is quite uncertain due to the possibility of land interaction, dry air entrainment, shear, and possible interaction with another system to the east. The intensity guidance again does not show much strengthening if Gamma emerges into the Gulf of Mexico, and that part of the new intensity forecast has only minor adjustments from the previous one. It should be noted that several models show a low pressure area over the northern Gulf of Mexico after 120 h. Whether this will be Gamma or a new system is unclear at this time. The biggest threat from this large and slow-moving storm is the the potential for heavy rainfall and flooding, particularly near and over mountainous terrain. KEY MESSAGES: 1. Gamma is expected to produce heavy rainfall that could result in life-threatening flash flooding over portions of the Yucatan Peninsula, far western Cuba and well away from the center in the Mexican states of Campeche, Tabasco, and northern Chiapas. 2. Gamma is forecast to bring tropical storm conditions to portions of the Yucatan Peninsula today and Sunday, where a Tropical Storm Warning is in effect. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 19.4N 86.9W 45 KT 50 MPH 12H 03/1800Z 20.2N 87.4W 50 KT 60 MPH 24H 04/0600Z 21.1N 87.9W 45 KT 50 MPH...INLAND 36H 04/1800Z 21.7N 88.0W 40 KT 45 MPH...OVER WATER 48H 05/0600Z 21.8N 88.4W 40 KT 45 MPH 60H 05/1800Z 21.6N 89.3W 45 KT 50 MPH 72H 06/0600Z 21.2N 90.5W 45 KT 50 MPH 96H 07/0600Z 20.5N 92.4W 45 KT 50 MPH 120H 08/0600Z 19.5N 93.5W 40 KT 45 MPH $$ Forecaster Beven

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Hurricane Marie Forecast Discussion Number 17

2020-10-03 10:38:20| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sat Oct 03 2020 122 WTPZ43 KNHC 030838 TCDEP3 Hurricane Marie Discussion Number 17 NWS National Hurricane Center Miami FL EP182020 200 AM PDT Sat Oct 03 2020 Marie continues to be a powerful and dangerous hurricane. Cloud tops surrounding the eye have cooled and the center is now surrounded by a ring of convection with tops colder than -70 degrees C. The latest Dvorak intensity estimate ranges have narrowed considerably to 115-122 kt, so there is higher confidence in the cyclone's strength. The initial advisory intensity is being kept at 115 kt and is in agreement with both of the subjective Dvorak estimates from TAFB and SAB. The environment surrounding Marie will soon become rather hostile and the hurricane will likely not maintain this intensity for much longer. By later today, increasing southwesterly winds aloft should begin to degrade the symmetry of the cyclone. Later tonight, the cyclone is forecast to cross the 26 degree C SST isotherm. And by Monday, Marie is expected be in an environment characterized by vertical wind shear greater than 30 kt, low- to mid-level relative humidity values of less than 40 percent, and over waters cooler than 25 degrees C. These increasingly negative factors are expected to cause Marie to begin weakening later today, with rapid weakening possible Sunday into Monday. The latest NHC intensity forecast is in good agreement with the various consensus intensity guidance, and indicates that Marie should weaken to a tropical storm on Sunday night and a tropical depression early next week. By the end of the forecast period, the system is expected to become a post tropical cyclone devoid of deep convection. Marie continues to move northwestward and is forecast to continue to do so through the remainder of the weekend as it moves along the southwest periphery of a mid-level ridge. The ridge is forecast to expand westward early next week, which should force the cyclone to turn to the west-northwest. Toward the end of the 5-day forecast period, a large deep-layer trough north of Marie should cause it to begin a turn to the right. The NHC track forecast is little changed from the previous one, and is close to the HFIP corrected consensus HCCA. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 17.9N 126.4W 115 KT 130 MPH 12H 03/1800Z 18.6N 127.2W 110 KT 125 MPH 24H 04/0600Z 19.5N 128.2W 90 KT 105 MPH 36H 04/1800Z 20.3N 129.2W 75 KT 85 MPH 48H 05/0600Z 20.9N 130.5W 60 KT 70 MPH 60H 05/1800Z 21.5N 131.9W 50 KT 60 MPH 72H 06/0600Z 22.0N 133.1W 40 KT 45 MPH 96H 07/0600Z 23.0N 135.3W 30 KT 35 MPH 120H 08/0600Z 24.5N 136.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Latto

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Hurricane Marie Forecast Discussion Number 16

2020-10-03 04:38:50| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Fri Oct 02 2020 000 WTPZ43 KNHC 030238 TCDEP3 Hurricane Marie Discussion Number 16 NWS National Hurricane Center Miami FL EP182020 800 PM PDT Fri Oct 02 2020 Although Marie still has an impressive and very symetric appearance, cloud tops associated with the huricane have gradually warmed since this afternoon and its eye became less well-defined for a brief period earlier this evening. The cause of this recent trend is not immediately clear since Marie is still located within a favorable low-shear, high SST environment, and two microwave passses near 00Z (SSMIS and SSMI) did not show any sign of an eyewall replacement cycle. Whatever the reason, it has caused intensity estimates to decrease a little since the last advisory, but not enough to justify lowering the intensity at this time. The intial intensity therefore remains 115 kt for this advisory. With a range of estimates from 90 kt to 127 kt, there is a lot of uncertainty in this assessment. Although Marie is located in a favorable environment for now, that won't last much longer. The hurricane is moving toward colder waters and it should begin to experience a large increase in wind shear within the next day or so. The guidance unsurprisingly forecasts that weakening will occur, possibly at a very rapid rate. The NHC forecast is on the high side of the intensity guidance, but still shows Marie becoming a tropical storm within 60 h and a depression by the end of the 5 day period. No changes of note were made to the offficial intensity forecast. Marie has turned northwestward, and should continue on that general heading for most of the weekend as it moves along the southwest periphary of a mid-level ridge. A slight expansion of the ridge could steer Marie more west-northwestward for a day or two after that. Around day 5, a large deep-layer trough should cause the cyclone to turn nearly northward. While there is considerable spread in the track guidance, limiting confidence in the specifics of the track forecast, every global model forecasts that general evolution. The NHC track forecast is very close to the model consensus and the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 17.5N 125.7W 115 KT 130 MPH 12H 03/1200Z 18.3N 126.8W 110 KT 125 MPH 24H 04/0000Z 19.2N 127.8W 95 KT 110 MPH 36H 04/1200Z 20.0N 128.8W 80 KT 90 MPH 48H 05/0000Z 20.6N 129.9W 65 KT 75 MPH 60H 05/1200Z 21.1N 131.4W 55 KT 65 MPH 72H 06/0000Z 21.6N 132.7W 45 KT 50 MPH 96H 07/0000Z 22.5N 134.8W 35 KT 40 MPH 120H 08/0000Z 24.0N 136.0W 30 KT 35 MPH $$ Forecaster Zelinsky

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Hurricane Marie Forecast Discussion Number 15

2020-10-02 22:41:59| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Fri Oct 02 2020 000 WTPZ43 KNHC 022041 TCDEP3 Hurricane Marie Discussion Number 15 NWS National Hurricane Center Miami FL EP182020 200 PM PDT Fri Oct 02 2020 Marie remains a powerful hurricane this afternoon. A 1530 UTC SSMIS 91 GHz microwave image showed a well-defined, closed eyewall with a 20 nm eye, which is still evident in recent GOES-17 visible and infrared satellite imagery. The initial intensity is held at 115 kt based on T6.0 Dvorak classifications from TAFB and SAB, which are consistent with recent ADT and earlier SATCON estimates. The 34-kt radii are expanded slightly with this package based on recent ASCAT data. Marie is moving west-northwestward (295 degrees) at 10 kt, around the southwestern periphery of a mid-level ridge centered over the southwestern United States. A break in the ridge should allow Marie to turn northwestward within the next 24 hours and maintain that motion over the next several days. By day 5, an approaching upper-level trough moving across the eastern Pacific Ocean should turn Marie more toward the north-northwest. There is still more noticeable spread in the guidance at days 4 and 5, likely related to differences in the amplitude of the upper-level trough. It is worth noting that the GFS depicts a deeper upper trough, and thus a more drastic northerly turn, than the rest of the global models. Overall, the NHC forecast was again slowed down a bit and shifted slightly to the right to align better with the latest TVCE multi-model consensus and HCCA aids. Marie is expected to remain in a low-shear environment with sea surface temperatures of 26 degrees Celsius for the next 18-24 hours. Although slight additional strengthening cannot be ruled out, the storm is running out of time before environmental conditions become more hostile. After 24 hours, increasing deep-layer southwesterly shear and cooler waters should support a steady weakening trend through the rest of the forecast period. Marie is expected to fall below hurricane strength by 60 hours and become a tropical depression by day 5. The latest NHC intensity forecast shows a slightly faster weakening trend and remains very close to the IVCN consensus and the HCCA aid. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 16.9N 125.0W 115 KT 130 MPH 12H 03/0600Z 17.6N 126.1W 115 KT 130 MPH 24H 03/1800Z 18.6N 127.4W 105 KT 120 MPH 36H 04/0600Z 19.5N 128.4W 90 KT 105 MPH 48H 04/1800Z 20.1N 129.5W 70 KT 80 MPH 60H 05/0600Z 20.6N 130.8W 60 KT 70 MPH 72H 05/1800Z 21.2N 132.1W 55 KT 65 MPH 96H 06/1800Z 22.0N 134.5W 35 KT 40 MPH 120H 07/1800Z 23.5N 136.0W 30 KT 35 MPH $$ Forecaster Reinhart/Berg

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