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Tropical Storm Beta Forecast Discussion Number 14

2020-09-21 04:47:08| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Sun Sep 20 2020 000 WTNT42 KNHC 210247 TCDAT2 Tropical Storm Beta Discussion Number 14 NWS National Hurricane Center Miami FL AL222020 1000 PM CDT Sun Sep 20 2020 Satellite and radar imagery shows that the deep convection associated with Beta has decreased considerably since this afternoon. This appears to be the result of dry air entrainment and vertical wind shear. Despite the recent decrease in convective organization, an Air Force Reserve Hurricane Hunter aircraft has found SFMR winds of around 45 kt, and there have been a couple of ship observations this evening of winds of 45-50 kt. Therefore, the initial intensity of 50 kt has been maintained. Data from the most recent center dropwindsonde indicate that the pressure is around 995 mb. Beta is forecast to remain within an area of moderate vertical wind shear, and that along with intrusions of dry air are likely to prevent Beta from strengthening before it nears the Texas coast. As a result, the NHC intensity forecast shows little change in strength before landfall in about 24 hours. Gradual weakening should occur after the center moves over land, but the weakening rate may be slower-than-normal as a portion of the circulation will remain offshore. In 2-3 days, the system is expected to weaken to a tropical depression, and it should become a remnant low by 96 h as it move farther inland over the lower Mississippi Valley. The NHC intensity forecast is near the upper-end of the intensity guidance through 24 hours, and is in best agreement with the SHIPS statistical model. Beta has jogged westward this evening, but the longer-term motion estimate is 290/5 kt. There is once again no change the previous track forecast philosophy. The tropical storm is located between a mid-level ridge over Florida and another ridge over the Southern Plains. Beta should move slowly west-northwestward toward the coast of Texas during the next 12 to 24 hours. After that time, the ridge over the Plains should weaken allowing the ridge to the east to steer Beta northward, and then northeastward near the Upper-Texas coast by mid-week. With the recent westward jog, the new track forecast has been nudged slightly south of the previous track through 24 hours, but is slightly east of the previous advisory thereafter to be closer to the various consensus aids. Key Messages: 1. The expected slow motion of Beta will produce a long duration rainfall event from the middle Texas coast to southern Louisiana. Flash, urban, and river flooding is likely. Rainfall will also spread northward into the ArkLaTex region and east into the Lower Mississippi Valley where flash, urban, and river flooding is possible. 2. There is the danger of life-threatening storm surge near times of high tide through Tuesday along portions of the Texas and Louisiana coasts within the storm surge warning areas. Residents in these areas should follow advice given by local officials. 3. Tropical-storm-force winds are occurring along portions of the northwestern Gulf Coast within the tropical storm warning area in Louisiana. These winds will spread westward to the Texas coast overnight and Monday. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 27.6N 94.5W 50 KT 60 MPH 12H 21/1200Z 28.0N 95.4W 50 KT 60 MPH 24H 22/0000Z 28.5N 96.4W 45 KT 50 MPH 36H 22/1200Z 28.8N 96.7W 35 KT 40 MPH...INLAND 48H 23/0000Z 29.1N 96.2W 30 KT 35 MPH...INLAND 60H 23/1200Z 29.5N 95.2W 30 KT 35 MPH...INLAND 72H 24/0000Z 30.1N 94.0W 30 KT 35 MPH...INLAND 96H 25/0000Z 31.9N 91.6W 20 KT 25 MPH...POST-TROP/INLAND 120H 26/0000Z...DISSIPATED $$ Forecaster Brown

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Remnants of Wilfred Forecast Discussion Number 11

2020-09-21 04:33:07| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sun Sep 20 2020 000 WTNT43 KNHC 210233 TCDAT3 Remnants Of Wilfred Discussion Number 11 NWS National Hurricane Center Miami FL AL232020 1100 PM AST Sun Sep 20 2020 Northwesterly vertical wind shear has continued to take a toll on Wilfred. Recent infrared satellite imagery along with scatterometer data indicate that Wilfred's low-level circulation has become an open trough of low pressure. Therefore, Wilfred is no longer a tropical cyclone and this will be the last NHC advisory on this system. The remaining deep convection has a linear shape and appears to be the result of the system interacting with an upper-level trough to its northwest. The scatterometer data revealed peak winds of close to 30 kt to the north of the trough axis, and that is the basis for the initial intensity. The system is moving generally westward at about 15 kt. The trough should continue to move westward at a slightly slower forward speed until it weakens and dissipates within a few days. This is the last NHC advisory on Wilfred. Additional information on the remnants of this system can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and online at ocean.weather.gov/shtml/NFDHSFAT1.php FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 15.9N 47.4W 30 KT 35 MPH 12H 21/1200Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm Beta Forecast Discussion Number 13

2020-09-20 22:57:35| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Sun Sep 20 2020 000 WTNT42 KNHC 202057 TCDAT2 Tropical Storm Beta Discussion Number 13 NWS National Hurricane Center Miami FL AL222020 400 PM CDT Sun Sep 20 2020 After a short-lived intense burst of deep convection a couple of hours ago, which helped to spin up a mid-level eye feature in radar imagery, Beta's convection has waned somewhat and the eye feature has become less distinct. Doppler velocity values of 60-65 kt between 15,000-20,000 ft were noted when the vortex column looked its best, but that spin up of the circulation also generated a significant amount of dry air entrainment that is now evident by a pronounced slot wrapping into the center from the north and northeast, which has likely caused the recent decrease in the inner-core convection. An Air Force Reserve reconnaissance aircraft was investigating Beta during the time of the aforementioned convective burst, and the low-level center was located about 18-20 nmi east of the radar eye feature, and the surface dropsonde measured west winds of 39 kt beneath the calm 850-mb center. These data indicate that vortex column possesses a significant amount of vertical tilt, which is not suggestive of an intensifying tropical cyclone. The aircraft found that the central pressure has remained at around 996 mb and also measured an 850-mb flight-level maximum wind of 60 kt, thus the initial intensity is being held at 50 kt. After accounting for the westward jump in the low-level center due to its recent reformation, the initial motion estimate is 295/05 kt. There is no significant change to the previous forecast track or reasoning. Beta is expected to remain within weak steering currents for the next couple of days, caught between a mid-level ridge over Florida and a weaker ridge located over the U.S. Southern Plains. Thereafter, the ridge over Florida become the dominant steering feature by amplifying northward and northwestward across the southeastern U.S. by early Tuesday, nudging Beta northward by late Tuesday, then followed by a faster northeastward motion on Wednesday through Friday. Due to the continued southwest to westerly shear expected to affect the cyclone, which will keep the convection and associated best pressure falls confined to the northeastern and eastern quadrants or near the Texas coast. As the result, the new NHC forecast track lies near the previous advisory track, and it located along the right side of the track guidance envelope, but not as far right as the new GFS-ECMWF (GFEX) consensus model. which keeps Beta over water for the next several days. Excluding the recent weakening of the vertical wind shear, which allowed Beta to undergo that bursting phase, the cyclone is forecast to remain under the influence of 15-20 kt or greater deep-layer shear throughout the forecast period, which is strong enough to keep the cyclone from strengthening much, but not enough to weaken or dissipate the cyclone before landfall occurs in 24 hours or so. Therefore, the intensity is expected to remain steady at 50 kt until landfall, although 5-kt fluctuations could occur which are in the forecast statistical noise. Slower-than-normal weakening for an inland tropical cyclone is expected due to Beta's proximity to the Gulf where brisk onshore flow could bring strong squalls over the Gulf into the coast. By day 3, Beta should weaken fairly quickly into a remnant low since the system will be located much farther and away from the influence of the Gulf of Mexico. The cyclone is expected to degenerate into a remnant low pressure system by early Wednesday and dissipate inland over the lower Mississippi Valley area by late Friday or Saturday. The intensity model guidance remains in good agreement on this developing forecast scenario, so no significant changes were made to the previous intensity forecast. Key Messages: 1. The expected slow motion of Beta will produce a long duration rainfall event from the middle Texas coast to southern Louisiana. Flash, urban, and river flooding is likely. Rainfall will also spread northward into the ArkLaTex region and east into the Lower Mississippi Valley where flash, urban, and river flooding is possible. 2. There is the danger of life-threatening storm surge near times of high tide through Tuesday along portions of the Texas and Louisiana coasts within the storm surge warning areas. Residents in these areas should follow advice given by local officials. 3. Tropical-storm-force winds are occurring along portions of the northwestern Gulf Coast within the tropical storm warning area in Louisiana. These winds will spread westward to the Texas coast later today and Monday. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 27.7N 94.0W 50 KT 60 MPH 12H 21/0600Z 28.1N 95.0W 50 KT 60 MPH 24H 21/1800Z 28.6N 96.1W 50 KT 60 MPH 36H 22/0600Z 29.0N 96.7W 45 KT 50 MPH...INLAND 48H 22/1800Z 29.4N 96.4W 40 KT 45 MPH...INLAND 60H 23/0600Z 29.7N 95.7W 35 KT 40 MPH...INLAND 72H 23/1800Z 30.0N 94.7W 30 KT 35 MPH...INLAND 96H 24/1800Z 32.0N 91.8W 20 KT 25 MPH...POST-TROP/INLAND 120H 25/1800Z 34.4N 89.5W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Stewart

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Hurricane Teddy Forecast Discussion Number 34

2020-09-20 22:56:35| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sun Sep 20 2020 542 WTNT45 KNHC 202056 TCDAT5 Hurricane Teddy Discussion Number 34 NWS National Hurricane Center Miami FL AL202020 500 PM AST Sun Sep 20 2020 Satellite images show that Teddy is continuing to maintain a central core, albeit eroded on the western side due to shear and dry air. However, the latest microwave data show a more distinct eye than conventional data would indicate, along with an open eyewall. The initial intensity is held at 90 kt, pending Air Force Reserve Hurricane Hunter aircraft data this evening. The hurricane has turned north-northwestward and is likely to turn northward tonight and north-northeastward tomorrow due to an approaching large mid-latitude trough. By early Tuesday, the cyclone should turn back to the north-northwest as it rotates around the same trough, then turn northeastward early Wednesday ahead of yet another trough moving into from eastern Canada. Track model guidance remains in very good agreement, and only a slight westward adjustment was made to the forecast. The global models are in excellent agreement on Teddy transitioning into a large non-tropical low between Bermuda and Nova Scotia in about 2 days. In many respects, the upcoming trough interaction reminds me of an extratropical transition like Sandy 2012, thankfully happening at a good distance from land, with the GFS/ECMWF models showing pressures into the 940s tomorrow, a slight increase in maximum winds, and a large increase in the size of the tropical-storm-force winds. Beyond Tuesday, the hurricane should become post-tropical near or south of Nova Scotia and be absorbed by a larger extratropical low after day 4 to the northeast of Newfoundland. Little change was made to the official forecast, other than show a small increase tomorrow as the peak extratropical forcing deepens the cyclone. It is still worth noting every model has a rather large and strong post-tropical cyclone near Nova Scotia in 2-3 days, with hazards that will extend a very long way from the center. Extremely dangerous surf conditions with 20-ft waves have been reported on the south shore of Bermuda, and officials are encouraging residents to avoid going into or near the water. Key Messages: 1. The center of Teddy is forecast to move east of Bermuda on Monday. Tropical storm conditions are likely on the island beginning this evening and could continue into Monday evening. 2. Teddy is expected to transition to a powerful post-tropical cyclone as it moves near or over portions of Atlantic Canada late Tuesday through Thursday, where there is an increasing risk of direct impacts from wind, rain, and storm surge. A Tropical Storm Watch has been issued for portions of Nova Scotia, and heavy rain is also expected across sections of Atlantic Canada. 3. Large swells produced by Teddy are expected to affect portions of Bermuda, the Leeward Islands, the Greater Antilles, the Bahamas, the east coast of the United States, and Atlantic Canada during the next few days. These swells could cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 29.0N 63.4W 90 KT 105 MPH 12H 21/0600Z 30.1N 63.5W 85 KT 100 MPH 24H 21/1800Z 32.8N 62.6W 90 KT 105 MPH 36H 22/0600Z 36.9N 63.0W 90 KT 105 MPH 48H 22/1800Z 40.0N 64.0W 85 KT 100 MPH 60H 23/0600Z 42.7N 63.5W 75 KT 85 MPH...POST-TROP/INLAND 72H 23/1800Z 46.0N 61.3W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 24/1800Z 54.5N 50.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 25/1800Z...DISSIPATED $$ Forecaster Blake

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Tropical Depression Seventeen-E Forecast Discussion Number 1

2020-09-20 22:54:05| Tropical Depression LIDIA

Issued at 300 PM MDT Sun Sep 20 2020

Tags: number discussion tropical depression

 

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