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Hurricane Dorian Forecast Discussion Number 20

2019-08-29 10:43:40| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Aug 29 2019 000 WTNT45 KNHC 290843 TCDAT5 Hurricane Dorian Discussion Number 20 NWS National Hurricane Center Miami FL AL052019 500 AM AST Thu Aug 29 2019 Soon after the previous advisory was issued, Dorian appeared to have a bit of a hiccup in its structure. A dry slot was noted penetrating into the southeastern portion of the circulation, with the eye becoming cloud- and rain-filled. In fact, dropsonde data from the Air Force Reserve mission indicated that the central pressure had come back up a bit to around 991 mb. That being said, the plane still measured maximum SFMR winds between 70-75 kt, so the initial intensity is being held steady at 75 kt for this advisory. Dorian continues northwestward, or 325 degrees at 11 kt. Confidence in the track forecast is fairly high for the first 48 hours, with Dorian expected to continue moving northwestward and then begin to turn west-northwestward between mid-level ridging to the north and a mid- to upper-level low retrograding westward across the Straits of Florida. The models, and their ensembles, continue to diverge after 48 hours and have not really budged from their respective solutions compared to yesterday. The GFS is a northern outlier from the rest of the guidance, showing a weaker ridge and bringing Dorian close to the Florida/Georgia border, while the UKMET and ECMWF models show stronger ridges and remain the southernmost solutions near South Florida. Given the spread in the guidance, the new NHC forecast blends the previous forecast with the simple multi-model consensus aids and the HCCA and Florida State Superensemble aids, and it actually ends up in a position very close to the tightly clustered global model ensemble means. The most notable change in the new forecast is that it's a little bit slower than the previous one as Dorian approaches Florida. Various shear analyses are indicating 10-15 kt of southwesterly shear over Dorian at the moment, but the global models show this shear diminishing within 12-24 hours. With lower shear and very warm waters, all of the intensity models forecast Dorian to begin strengthening again soon, and rapid intensification could occur. The updated NHC intensity forecast has been increased from the previous one and most closely follows the HCCA and Florida State Superensemble aids during the first day or two. After 48 hours, the official forecast is near or just above the intensity consensus, but it's still lower than the solutions shown by the HCCA, Florida State Superensemble, and the HWRF. Dorian is likely to reach major hurricane strength in the next day or two and is forecast to maintain that status until it reaches land. Key Messages: 1. The risk of dangerous storm surge and hurricane-force winds later this week and this weekend continues to increase in the central and northwestern Bahamas and along the Florida east coast, although it is too soon to determine where these hazards will occur. Residents in these areas should ensure they have their hurricane plan in place and not focus on the exact forecast track of Dorian's center. 2. Heavy rains are expected to occur over portions of the Bahamas, Florida, and elsewhere in the southeastern United States later this week and into early next week. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 20.5N 66.6W 75 KT 85 MPH 12H 29/1800Z 21.9N 67.6W 85 KT 100 MPH 24H 30/0600Z 23.7N 69.0W 95 KT 110 MPH 36H 30/1800Z 25.1N 70.6W 100 KT 115 MPH 48H 31/0600Z 26.0N 72.5W 105 KT 120 MPH 72H 01/0600Z 27.0N 76.4W 110 KT 125 MPH 96H 02/0600Z 27.5N 79.5W 110 KT 125 MPH 120H 03/0600Z 28.0N 81.5W 75 KT 85 MPH...INLAND $$ Forecaster Berg

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Post-Tropical Cyclone Erin Forecast Discussion Number 11

2019-08-29 10:40:47| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Thu Aug 29 2019 000 WTNT41 KNHC 290840 TCDAT1 Post-Tropical Cyclone Erin Discussion Number 11 NWS National Hurricane Center Miami FL AL062019 500 AM EDT Thu Aug 29 2019 Satellite imagery and scatterometer data indicate that Erin is merging with a frontal system and is now an extratropical low. The low is expected to accelerate northeastward toward Nova Scotia over the next 24 h, and some slight intensification is expected during that time. After 24 h, the system is expected to be absorbed by a larger extratropical low over eastern Canada. This is the last advisory on Erin from the National Hurricane Center. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service...under AWIPS header NFDHSFAT1 and WMO header FZNT01 KWBC. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 36.1N 71.6W 30 KT 35 MPH...POST-TROP/EXTRATROP 12H 29/1800Z 39.3N 69.3W 30 KT 35 MPH...POST-TROP/EXTRATROP 24H 30/0600Z 44.3N 64.9W 35 KT 40 MPH...POST-TROP/EXTRATROP 36H 30/1800Z...POST-TROP/EXTRATROP $$ Forecaster Beven

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Hurricane Dorian Forecast Discussion Number 19

2019-08-29 04:39:47| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Aug 28 2019 000 WTNT45 KNHC 290239 TCDAT5 Hurricane Dorian Discussion Number 19 NWS National Hurricane Center Miami FL AL052019 1100 PM AST Wed Aug 28 2019 Data from an Air Force Reserve Unit Hurricane Hunter aircraft indicate that Dorian has intensified, and San Juan radar data show that the eye is becoming better defined. Based on SFMR-observed surface wind observations from the aircraft, the intensity is increased to 75 kt. Dorian should remain in an environment of low shear, within a moistening mid-level air mass, and over SSTs near 29 deg C for the next several days. This should allow for Dorian to intensify into a major hurricane. The official intensity forecast is similar to the previous one, and close to the latest DSHIPS model output. The initial motion estimate remains northwestward, or 320/11 kt. Dorian should continue to move northwestward toward a weakness in the subtropical ridge over the next couple of days. Later in the forecast period, a ridge builds over the western Atlantic. This evolution of the steering pattern should cause Dorian to turn west-northwestward and head for the Florida peninsula. The actual track of the hurricane in 3 to 5 days will depend on how much the western Atlantic ridge builds during that time frame. This is, of course, subject to uncertainty. The official track forecast is very similar to the previous one, and close to the latest simple and corrected dynamical model consensus. Key Messages: 1. The risk of dangerous storm surge and hurricane-force winds later this week and this weekend continues to increase in the central and northwestern Bahamas and along the Florida east coast, although it is too soon to determine where these hazards will occur. Residents in these areas should ensure they have their hurricane plan in place and not focus on the exact forecast track of Dorian's center. 2. Heavy rains are expected to occur over portions of the Bahamas, Florida, and elsewhere in the southeastern United States later this week and into early next week. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 19.7N 66.0W 75 KT 85 MPH 12H 29/1200Z 21.0N 67.0W 80 KT 90 MPH 24H 30/0000Z 22.9N 68.3W 85 KT 100 MPH 36H 30/1200Z 24.5N 69.9W 90 KT 105 MPH 48H 31/0000Z 25.7N 71.7W 95 KT 110 MPH 72H 01/0000Z 27.0N 75.8W 100 KT 115 MPH 96H 02/0000Z 27.8N 79.4W 100 KT 115 MPH 120H 03/0000Z 28.4N 81.8W 80 KT 90 MPH...INLAND $$ Forecaster Pasch

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Tropical Depression Erin Forecast Discussion Number 10

2019-08-29 04:38:40| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Wed Aug 28 2019 000 WTNT41 KNHC 290238 TCDAT1 Tropical Depression Erin Discussion Number 10 NWS National Hurricane Center Miami FL AL062019 1100 PM EDT Wed Aug 28 2019 After being devoid of deep convection for much of the day, new convection has developed around the center of Erin's circulation over the past couple of hours, giving it a little more time as a tropical cyclone. The current objective Dvorak intensity estimate from TAFB is 30 kt, and so that will remain the initial intensity for this advisory. Westerly shear should prevent any intensification of Erin while it remains a tropical cyclone tonight. On Thursday, the cyclone should merge with a frontal system while it undergoes extratropical transition. Thereafter, the merged system could strengthen due to baroclinic processes. Erin has accelerated and is now moving at 025/18 kt. The cyclone is expected to move even faster to the northeast on Thursday and continue northeastward until it merges with another extratropical low by late Friday. The updated NHC track forecast is changed little from the previous advisory, and lies near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 35.6N 72.1W 30 KT 35 MPH 12H 29/1200Z 38.0N 70.6W 30 KT 35 MPH...POST-TROP/EXTRATROP 24H 30/0000Z 42.4N 66.8W 35 KT 40 MPH...POST-TROP/EXTRATROP 36H 30/1200Z 47.3N 62.2W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 31/0000Z...DISSIPATED $$ Forecaster Latto/Pasch

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Hurricane Dorian Forecast Discussion Number 18

2019-08-28 22:45:05| National Hurricane Center (Atlantic)

Issued at 500 PM AST Wed Aug 28 2019 000 WTNT45 KNHC 282044 TCDAT5 Hurricane Dorian Discussion Number 18 NWS National Hurricane Center Miami FL AL052019 500 PM AST Wed Aug 28 2019 The cloud pattern has become better organized with a hint of an eye on high resolution satellite imagery and plenty of convective bands. In addition, earlier data from a reconnaissance plane and surface observations from St. Thomas as Dorian moved by yield an initial intensity of 70 kt. Now that the hurricane has developed an inner core with a 15 to 20 n mi eye, strengthening is more likely. Given the favorable environment of warm waters and low shear prevailing in the western Atlantic, the NHC forecast calls for a marked intensification, and brings Dorian to category 3 intensity in 72 hours, and keeps it at that intensity until landfall. This forecast is very close to the intensity consensus, the HCCA model, and the SHIPS guidance. Satellite and earlier reconnaissance plane fixes indicate that Dorian has been moving toward the northwest or 320 degrees at 12 kt. The cyclone is heading toward a weakness in the Atlantic subtropical ridge, and this northwest motion should continue for the next 24 to 48 hours. However, after that time, all the global models continue to build a strong ridge over the western Atlantic, and this flow pattern should force Dorian to turn more to the west-northwest toward Florida. All indications are that by this Labor Day weekend, a powerful hurricane will be near or over the Florida peninsula. The new NHC track forecast is a little bit to the south of the previous one, given that global models have a stronger ridge to the north and the track models show more of a westward motion. Users are reminded not to focus on the exact forecast track, as the average 5-day track error is around 200 miles. Key Messages: 1. Dangerous winds will continue in the Virgin Islands, Culebra, Vieques, and portions of Puerto Rico during the next few hours. Heavy rainfall over portions of Puerto Rico and the Virgin Islands could produce flash flooding through Thursday morning. 2. The risk of dangerous storm surge and hurricane-force winds later this week and this weekend continues to increase in the central and northwestern Bahamas and along the Florida east coast, although it is too soon to determine where these hazards will occur. Residents in these areas should ensure they have their hurricane plan in place and not focus on the exact forecast track of Dorian's center. 3. Heavy rains are expected to occur over portions of the Bahamas, Florida, and elsewhere in the southeastern United States later this week and into early next week. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 18.8N 65.5W 70 KT 80 MPH 12H 29/0600Z 20.1N 66.6W 75 KT 85 MPH 24H 29/1800Z 22.0N 68.0W 80 KT 90 MPH 36H 30/0600Z 23.8N 69.3W 85 KT 100 MPH 48H 30/1800Z 25.2N 71.1W 90 KT 105 MPH 72H 31/1800Z 26.8N 75.0W 100 KT 115 MPH 96H 01/1800Z 27.7N 79.0W 100 KT 115 MPH 120H 02/1800Z 28.2N 81.5W 85 KT 100 MPH...INLAND $$ Forecaster Avila

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