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Hurricane Leslie Forecast Discussion Number 61

2018-10-11 16:44:44| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Oct 11 2018 000 WTNT43 KNHC 111444 TCDAT3 Hurricane Leslie Discussion Number 61 NWS National Hurricane Center Miami FL AL132018 1100 AM AST Thu Oct 11 2018 Leslie's structure has remained steady since last night. The hurricane has a ragged banding eye surrounded by a somewhat patchy central dense overcast. Recent Dvorak classifications from TAFB and SAB are unchanged, and still support an initial intensity of 70 kt. For days now, it has been clear that Leslie will accelerate east-northeastward on the south side of a mid-latitude trough moving across the North Atlantic. That acceleration is well underway now, and the initial motion estimate is 060/14 kt. It has been unclear, however, when (or if) Leslie could separate from this trough and begin to drift southward over the eastern Atlantic. The model spread has remarkably increased since yesterday, and nearly 1/3 of the members of the most recent GFS and ECMWF ensemble runs no longer forecast Leslie to separate from the trough at all, instead showing the cyclone approaching western Europe as an extratropical low. Even the deterministic model spread has increased, and the two NOAA regional hurricane models, the HWRF and HMON, are nearly 2300 miles apart at day 5. Through 48 h, the official track forecast is very similar to the previous advisory, but it has been adjusted eastward beyond that time, to bring it closer to the most recent deterministic multi-model consensus. Confidence in the track forecast is not high at 72 h and beyond, and it's possible that large changes could still be required to future advisories. Leslie should remain in a generally favorable environment for strengthening during the next 24-36 h, and slight intensification is still expected, though the official intensity forecast is now on the high side of the guidance through this period. By 48 h and onward, Leslie will be moving into a far more stable environment and over cooler waters, so steady weakening is anticipated. If Leslie follows a track similar to the NHC forecast, it will likely become a weak post-tropical low within 96 h. However, if Leslie undergoes extratropical transition, its worth noting that the maximum winds associated with the cyclone would likely be higher than indicated here. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 29.1N 38.3W 70 KT 80 MPH 12H 12/0000Z 30.3N 35.5W 75 KT 85 MPH 24H 12/1200Z 31.7N 30.3W 75 KT 85 MPH 36H 13/0000Z 32.8N 24.6W 70 KT 80 MPH 48H 13/1200Z 33.2N 20.0W 60 KT 70 MPH 72H 14/1200Z 31.3N 17.3W 40 KT 45 MPH 96H 15/1200Z 29.1N 19.0W 30 KT 35 MPH...POST-TROPICAL 120H 16/1200Z 27.5N 24.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky

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Tropical Storm Sergio Forecast Discussion Number 49

2018-10-11 16:39:39| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Thu Oct 11 2018 000 WTPZ41 KNHC 111439 TCDEP1 Tropical Storm Sergio Discussion Number 49 NWS National Hurricane Center Miami FL EP212018 800 AM PDT Thu Oct 11 2018 The cloud pattern of Sergio continues to show organization with a couple of cyclonically curved hooking bands, however the convection in these bands is weak to moderate. Dvorak estimates suggest that the initial intensity still is 55 kt. Sergio is about to move over cooler waters and the shear is forecast to increase significantly, so the expected weakening process should begin later today. Nevertheless, the cyclone should still be a tropical storm when it moves over the Baja California peninsula, but it should dissipate once it moves over the high terrain of the Mexican mainland over the state of Sonora. Satellite fixes indicate that Sergio is moving toward the northeast about 17 kt. The storm is embedded within the deep-layer southwesterly flow associated with a broad mid-latitude trough located just off the U.S. west coast. This flow pattern will continue to steer Sergio toward the northeast with an increase in forward speed. Track models are in excellent agreement and unanimously bring Sergio over the central portion of the Baja California peninsula in about 24 hours and so does the official forecast. The primary threat associated with Sergio and its remnants continues to be life-threatening flash flooding and mudslides within mountainous terrain in the Mexico states of Baja California Sur, Sonora, the U.S. Southern Plains, and the Ozarks through the weekend. For more information about this potential hazard, see products from the Weather Prediction Center and your local weather forecast office. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 22.2N 118.7W 55 KT 65 MPH 12H 12/0000Z 24.2N 116.2W 50 KT 60 MPH 24H 12/1200Z 27.0N 113.0W 40 KT 45 MPH 36H 13/0000Z 29.5N 109.0W 25 KT 30 MPH...INLAND 48H 13/1200Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Nadine Forecast Discussion Number 9

2018-10-11 10:50:41| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Oct 11 2018 000 WTNT45 KNHC 110850 TCDAT5 Tropical Storm Nadine Discussion Number 9 NWS National Hurricane Center Miami FL AL152018 500 AM AST Thu Oct 11 2018 Nadine is a sheared tropical storm with the low-level center located near the western edge of the main area of deep convection. An ASCAT pass from several hours ago showed maximum winds in the 50-55 kt range, and since the satellite appearance has not changed much, the initial intensity is held at 55 kt. This value is near the high end of the satellite-based intensity estimates. The environment near Nadine is expected to become even more hostile during the next couple of days due to the combined effects of strong west- southwesterly shear and drier air. Therefore, steady weakening is forecast, and dissipation is expected to occur in 2 to 3 days when the shear is forecast to be in excess of 30 kt. The models are in good agreement, and little change was made to the previous NHC intensity forecast. The storm is moving northwestward at 7 kt. The track forecast reasoning is unchanged from previous advisories. Nadine is expected to continue moving northwestward for about another day while the tropical storm remains relatively deep, or vertically coherent. After that time, the weakening and increasingly shallow cyclone is forecast to turn to the left in the low-level flow, and that motion should continue until the system dissipates. The NHC track forecast lies near the middle of the guidance envelope, and it is not too different than the previous one. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 14.1N 33.3W 55 KT 65 MPH 12H 11/1800Z 14.9N 34.1W 45 KT 50 MPH 24H 12/0600Z 15.7N 35.4W 40 KT 45 MPH 36H 12/1800Z 16.3N 37.0W 35 KT 40 MPH 48H 13/0600Z 16.7N 39.0W 30 KT 35 MPH 72H 14/0600Z...DISSIPATED $$ Forecaster Cangialosi

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Hurricane Leslie Forecast Discussion Number 60

2018-10-11 10:49:42| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Oct 11 2018 000 WTNT43 KNHC 110849 TCDAT3 Hurricane Leslie Discussion Number 60 NWS National Hurricane Center Miami FL AL132018 500 AM AST Thu Oct 11 2018 The cloud pattern of Leslie has not changed significantly overnight. The hurricane has a large and ragged eye with deep convection most organized on its east side. The Dvorak CI-numbers are unchanged at 4.0/65 kt from TAFB and 4.5/77 kt from SAB, and based on these data, the initial intensity is held at 70 kt. Leslie will remain in low wind shear conditions and over relatively warm waters for another day or two, so little change in strength is expected during that time. Thereafter, the hurricane is forecast to move over waters as cool as 24 deg C and into an atmospheric environment of stronger shear and drier air. All of these conditions point to a weakening trend, which is likely to begin by the weekend. Most of the guidance shows a cold front approaching Leslie, but not quite merging with it so extratropical transition is not expected. However, it seems likely that Leslie will lose its convection and become a weaker post-tropical low in about 4 days. This scenario is supported by the latest runs of the GFS, ECMWF, and HWRF models. Leslie has made the expected east-northeastward turn with the latest initial motion estimated to be 065/9. This east-northeastward motion with an increase in forward speed is forecast to continue for the next 2 days while the steering pattern holds. After that time, however, it becomes much less clear. The models continue to struggle and keep changing their tune cycle to cycle on whether or not Leslie continues east-northeastward toward Morocco or Portugal, or gets left behind and moves west-southwestward due to a building ridge. The ensemble members of both the GFS and ECMWF favor the left behind (or southwestward) solution, and the NHC track forecast continues to lean in that direction. This forecast does show Leslie moving farther east before it makes the southwestward turn to be in better agreement with the latest consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 28.4N 40.1W 70 KT 80 MPH 12H 11/1800Z 29.3N 37.8W 75 KT 85 MPH 24H 12/0600Z 30.9N 33.3W 75 KT 85 MPH 36H 12/1800Z 32.1N 27.5W 70 KT 80 MPH 48H 13/0600Z 32.7N 22.3W 70 KT 80 MPH 72H 14/0600Z 31.3N 18.7W 50 KT 60 MPH 96H 15/0600Z 29.0N 19.5W 35 KT 40 MPH...POST-TROPICAL 120H 16/0600Z 27.5N 24.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Tropical Storm Michael Forecast Discussion Number 19

2018-10-11 10:49:42| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Thu Oct 11 2018 000 WTNT44 KNHC 110849 TCDAT4 Tropical Storm Michael Discussion Number 19 NWS National Hurricane Center Miami FL AL142018 500 AM EDT Thu Oct 11 2018 Surface observations and WSR-88D Doppler radar data indicate that Michael continues to weaken as the center moves through eastern Georgia, and based on these data the initial intensity is decreased to 45 kt. There is currently a small area of tropical-storm-force winds near the center, with a second area over the Atlantic well to the southeast of the center. Michael should continue to weaken for the next 12 h or so as the center moves through South Carolina and into North Carolina. After that time, the cyclone should start to intensify due to baroclinic forcing, and it is expected to become a gale- or storm-force extratropical low around the 24-h point. The new intensity forecast is an update of the previous forecast, and it leans heavily on global model guidance during the extratropical phase. The initial motion is now 045/18. Michael will accelerate toward the northeast and east-northeast as it becomes further embedded in the mid-latitude westerlies. The new track forecast track is near the various consensus models and has no significant changes from the previous forecast. Gale- to storm-force winds are expected over portions of the Mid-Atlantic coast as Michael exits the U.S. east coast and becomes post-tropical. Non-tropical high wind watches, warnings, and advisories have been issued by local NWS offices for wind hazards in these areas north of Duck, North Carolina. Key Messages: 1. Heavy rainfall from Michael could produce life-threatening flash flooding over portions of Georgia, the Carolinas, and southeastern Virginia. 2. Tropical storm conditions will continue to affect portions of the southeast U.S. coast from Georgia through North Carolina, and tropical storm warnings remain in effect for these areas. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 33.5N 82.5W 45 KT 50 MPH...INLAND 12H 11/1800Z 35.4N 79.4W 40 KT 45 MPH...INLAND 24H 12/0600Z 37.9N 74.1W 45 KT 50 MPH...POST-TROP/EXTRATROP 36H 12/1800Z 40.9N 65.8W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 13/0600Z 44.1N 55.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 14/0600Z 48.0N 29.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 15/0600Z 49.0N 9.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 16/0600Z...DISSIPATED $$ Forecaster Beven

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