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Tropical Storm Beta Forecast Discussion Number 9

2020-09-19 23:00:42| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Sat Sep 19 2020 000 WTNT42 KNHC 192100 TCDAT2 Tropical Storm Beta Discussion Number 9 NWS National Hurricane Center Miami FL AL222020 400 PM CDT Sat Sep 19 2020 Satellite imagery indicates that Beta has a small area of convection over the low-level center, with a dry slot on the northeastern side separating that convection from a larger outer band. Satellite intensity estimates are generally in the 40-55 kt range and have changed little since the past advisory. In addition, a ship just north of the center just reported 47-kt winds and a pressure of 998.6 mb. Based on these data, the initial intensity remains 50 kt. Earlier scatterometer data showed a trough extending from near the center of Beta to just south of the mouth of the Mississippi River, which may be a result of the cyclone's circulation interacting with an old cold front over the northern Gulf. Beta has been nearly stationary since the last advisory, with the center perhaps making a small loop. The guidance is in good agreement that a slow westward to west-northwestward motion should start tonight as a mid-level ridge develops north of the cyclone. A slightly faster west-northwestward motion should then occur through 72 h, bringing the center of Beta near or over the Texas coast in about 60 h. After landfall, a mid-latitude trough moving through the central United States should cause Beta to recurve slowly to the northeast. Despite the current lack of movement, the latest track guidance is a little faster to bring the storm to the coast of Texas with the ECMWF forecasting landfall by 12Z Monday. The new forecast track is a little faster than the previous forecast, but is a little slower than the various consensus models. There remain a lot of uncertainties in the intensity forecast. First, the global models still suggest that the ongoing southwesterly shear may not subside much before landfall. Second, GOES-16 air mass imagery shows abundant upper-level dry air over the western Gulf of Mexico, including near the storm center. Third, surface observations show a drier low-level airmass in place over southeastern Texas, and some of this may be getting entrained into the storm. The intensity guidance has again trended downward, and several of the models now forecast Beta not to strengthen at all as it approaches Texas. Because the sea surface temperatures are warm and the shear is not prohibitively strong, the intensity forecast, while reduced from the earlier forecast, will show slow strengthening to a peak intensity of 60 kt before landfall. This forecast remains above the guidance, and additional downward adjustments may be needed tonight or on Sunday. While the chances that Beta will become a hurricane are decreasing, a Hurricane Warning could still be issued for portions of the Texas coast tonight depending on later intensity trends and forecasts. Key Messages: 1. The expected slow motion of Beta has the potential to produce a long duration rainfall event along the western Gulf Coast. The potentially prolonged period of rainfall could cause flash, urban, and river flooding, especially in coastal areas where tide levels are above normal. 2. There is the danger of life-threatening storm surge near times of high tide from Sunday through Tuesday along portions of the Texas coast within the storm surge warning areas. Residents in these areas should follow advice given by local officials. 3. Tropical storm force winds are expected to begin along portions of the northwestern Gulf Coast by Sunday night within the tropical storm warning area, with hurricane-force winds possible along portions of the Texas coast late Monday and Monday night, where a hurricane watch is in effect. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 26.6N 92.4W 50 KT 60 MPH 12H 20/0600Z 26.7N 93.1W 50 KT 60 MPH 24H 20/1800Z 27.1N 94.0W 55 KT 65 MPH 36H 21/0600Z 27.5N 95.1W 55 KT 65 MPH 48H 21/1800Z 27.9N 96.0W 60 KT 70 MPH 60H 22/0600Z 28.3N 96.4W 60 KT 70 MPH 72H 22/1800Z 28.8N 96.4W 50 KT 60 MPH...INLAND 96H 23/1800Z 29.5N 95.0W 35 KT 40 MPH...INLAND 120H 24/1800Z 31.0N 93.0W 25 KT 30 MPH...INLAND $$ Forecaster Beven

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Tropical Storm Wilfred Forecast Discussion Number 6

2020-09-19 22:33:11| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sat Sep 19 2020 000 WTNT43 KNHC 192033 TCDAT3 Tropical Storm Wilfred Discussion Number 6 NWS National Hurricane Center Miami FL AL232020 500 PM AST Sat Sep 19 2020 A small low-level swirl that is apparently Wilfred's circulation center was noted in late afternoon visible imagery. The coldest cloud tops are in a small area of bursting convection to the northeast of the center with a ragged convective band noted to the south and southwest. The latest objective and subjective satellite intensity estimates remain 35 kt, and that will be the intensity for this advisory, but could be a bit generous. Increasing westerly shear and a drying airmass along the forecast track should result in weakening within 36 to 48 hours, and global models show the cyclone dissipating by 60 h. However, given the small size of the system, it wouldn't be surprising if the cyclone weakened or dissipated sooner than shown here. The initial motion estimate is 290/12. Wilfred should continue west-northwestward for the next 24 to 36 hours before turning westward in the low-level flow prior to dissipation. The new NHC track forecast is close to the previous one and lies near the consensus aids and the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 14.0N 39.2W 35 KT 40 MPH 12H 20/0600Z 14.8N 41.3W 35 KT 40 MPH 24H 20/1800Z 15.6N 44.0W 35 KT 40 MPH 36H 21/0600Z 16.0N 46.6W 35 KT 40 MPH 48H 21/1800Z 16.2N 48.6W 30 KT 35 MPH 60H 22/0600Z...DISSIPATED $$ Forecaster Brennan

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Tropical Storm Beta Forecast Discussion Number 8

2020-09-19 17:38:30| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Sat Sep 19 2020 000 WTNT42 KNHC 191538 TCDAT2 Tropical Storm Beta Discussion Number 8...Corrected NWS National Hurricane Center Miami FL AL222020 1000 AM CDT Sat Sep 19 2020 Corrected 96 and 120 h intensities Morning visible imagery indicates that Beta has become significantly sheared, with the low-level center mostly exposed well to the southwest of the main convective area. A new convective band is currently forming near the center over the northwestern quadrant. An Air Force Reserve Hurricane Hunter aircraft reported pressures near 994-995 mb, along with flight-level and SFMR winds that justify keeping the initial intensity at 50 kt. The storm appears to be starting its westward turn, and the initial motion is now 315/3. The mid- to upper-level trough over the northwestern Gulf of Mexico is lifting out, with a mid-level ridge building to the north of Beta. This should cause the storm to turn more westward during the next 6-12 h. After that, a slow west- northwestward to northwestward motion should develop, with the center now forecast to be near or over the middle Texas coast in about 72 h. Beyond 72 h, another mid-latitude trough moving through the central United States should cause Beta to recurve slowly to the northeast. The new NHC forecast is shifted a little to the west and now explicitly shows landfall on the Texas coast in about 72 h. This new forecast is a little to the north of the consensus models through 72 h and close to them after that time. There are lots of uncertainties in the intensity forecast. First, the global models suggest that the ongoing southwesterly shear may not subside that much even though the first trough is lifting out. Second, GOES-16 air mass imagery shows abundant upper-level dry air over the western Gulf of Mexico, including near the storm center. Third, surface observations show a drier low-level airmass in place over southeastern Texas, and some of this may get entrained into the storm. The intensity guidance has trended downward to the point where none of the models are currently forecasting Beta to become a hurricane. Based on this and the current storm structure, the intensity forecast has been adjusted to show little change in strength today, followed by slow strengthening to a hurricane by 48-60 h. However, this forecast is well above the guidance, and additional downward adjustments may be needed later today. A Tropical Storm Warning is being issued for parts of the Texas and Louisiana coasts at this time. A Hurricane Warning could still be issued later today or tonight depending on later intensity forecasts. Key Messages: 1. The expected slow motion of Beta has the potential to produce a long duration rainfall event along the western Gulf Coast. The potentially prolonged period of rainfall could cause flash, urban, and river flooding, especially where tide levels are above normal. 2. Life-threatening storm surge and hurricane-force winds are possible along portions of the northwestern Gulf Coast, with tropical storm conditions expected by late this weekend. Storm Surge and Hurricane watches and Tropical Storm warnings are in effect, and residents in these areas should ensure they have their hurricane plan in place and follow advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 26.6N 92.6W 50 KT 60 MPH 12H 20/0000Z 26.9N 93.0W 50 KT 60 MPH 24H 20/1200Z 27.1N 93.8W 55 KT 65 MPH 36H 21/0000Z 27.5N 94.8W 60 KT 70 MPH 48H 21/1200Z 27.8N 95.5W 65 KT 75 MPH 60H 22/0000Z 28.2N 96.2W 65 KT 75 MPH 72H 22/1200Z 28.6N 96.2W 55 KT 65 MPH...INLAND 96H 23/1200Z 29.5N 95.0W 45 KT 50 MPH...INLAND 120H 24/1200Z 30.5N 93.0W 30 KT 35 MPH...INLAND $$ Forecaster Beven

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Hurricane Teddy Forecast Discussion Number 29

2020-09-19 16:51:03| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Sep 19 2020 000 WTNT45 KNHC 191450 TCDAT5 Hurricane Teddy Discussion Number 29 NWS National Hurricane Center Miami FL AL202020 1100 AM AST Sat Sep 19 2020 The overall appearance of Teddy has degraded slightly since early this morning, with the eye no longer readily apparent in satellite imagery. However, microwave data a few hours ago showed that a well- defined outer eyewall exists with a decaying partial inner eyewall. This indicates that an eyewall replacement cycle is just about complete. The objective and subjective satellite intensity estimates generally agree on an intensity of 98-102 kt, but out of respect for the completing eyewall replacement cycle the initial intensity is set to a slightly more generous 105 kt. Teddy will be moving over slightly cooler waters caused by upwelling from Paulette over the next day or so and this should cause the hurricane to slowly weaken. However, in about 36 h the cyclone's wind field is forecast to begin expanding as it interacts with an approaching frontal system. Around 48-60 h, vertical wind shear is expected to dramatically increase as Teddy becomes embedded in the flow around a sharp mid-latitude upper-level trough. The interaction of the cyclone with both the front and trough should cause Teddy to begin an extratropical transition, with the post-tropical cyclone quickly weakening once the transition is complete. The SHIPS guidance and global model simulated satellite imagery tend to agree that the extratropical transition should be completed just after 72 h. The latest NHC intensity forecast was nudged downward slightly mainly due to the change in the initial intensity, and is close to the HFIP corrected consensus HCCA. The hurricane continues its northwestward movement, now at 12 kt. The track forecast for Teddy remains essentially unchanged and is in the middle of tightly clustered guidance. Teddy is expected to turn northward to north-northeastward Sunday morning as it approaches a frontal system over the western Atlantic. This pattern should steer the hurricane east of Bermuda, though the hurricane's large wind field means that the island will still likely experience tropical storm conditions beginning by Sunday evening and continuing through much of Monday. A slight turn to the north then perhaps the north- northwest should occur Monday night into Tuesday as Teddy pivots around the upper trough. By Tuesday night, the cyclone is forecast to turn northeastward as the upper trough to its southwest begins to lift into the higher latitudes. Teddy is producing an extensive area of large waves and swells which are impacting much of the western Atlantic basin. See the Key Messages below. Key Messages: 1. While the center of Teddy is forecast to move east of Bermuda late Sunday or Monday, tropical storm conditions are likely on the island beginning Sunday afternoon or evening. 2. Teddy is expected to transition to a powerful post-tropical cyclone as it moves near or over portions of Atlantic Canada early next week, where there is an increasing risk of direct impacts from wind, rain, and storm surge. Residents there should closely monitor the progress of Teddy and updates to the forecast. 3. Large swells produced by Teddy are expected to affect portions of the Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, 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 19/1500Z 26.0N 59.0W 105 KT 120 MPH 12H 20/0000Z 27.3N 60.4W 100 KT 115 MPH 24H 20/1200Z 28.8N 61.7W 95 KT 110 MPH 36H 21/0000Z 30.4N 62.2W 90 KT 105 MPH 48H 21/1200Z 33.1N 61.6W 90 KT 105 MPH 60H 22/0000Z 37.1N 61.2W 90 KT 105 MPH 72H 22/1200Z 40.8N 61.8W 80 KT 90 MPH 96H 23/1200Z 47.0N 59.8W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 24/1200Z 52.9N 51.1W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto

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Tropical Storm Wilfred Forecast Discussion Number 5

2020-09-19 16:50:32| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Sep 19 2020 000 WTNT43 KNHC 191450 TCDAT3 Tropical Storm Wilfred Discussion Number 5 NWS National Hurricane Center Miami FL AL232020 1100 AM AST Sat Sep 19 2020 Wilfred still consists of a very small low-level circulation embedded within an elongated area of low pressure. There has been a bit of an increase in deep convection near/over the estimated center during the past few hours, and the intensity remains 35 kt based on the latest Dvorak classifications from TAFB and SAB and UW-CIMSS SATCON. Wilfred will be moving over SSTs of around 28C but will experience a gradual increase in westerly shear during the next 24 to 36 hours as an upper-level trough amplifies to the northwest, and this should result in little change in strength during that time. Beyond that time, the cyclone moves into a drier and more stable airmass, which should result in the system becoming a remnant low and dissipating in 60 to 72 hours. The new NHC intensity forecast is close to the latest IVCN consensus. The initial motion estimate based on the latest satellite fixes is 285/12. Wilfred should continue moving generally west- northwestward for the next 24 to 36 hours and then turn more westward by 48 h as it becomes a shallower system. The new NHC track forecast is a bit faster than the previous one and has been adjusted farther south at 36 h and beyond, trending toward the latest consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 13.4N 38.1W 35 KT 40 MPH 12H 20/0000Z 14.2N 40.2W 35 KT 40 MPH 24H 20/1200Z 15.2N 43.1W 35 KT 40 MPH 36H 21/0000Z 15.9N 45.8W 35 KT 40 MPH 48H 21/1200Z 16.2N 48.0W 30 KT 35 MPH 60H 22/0000Z 16.3N 49.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 22/1200Z...DISSIPATED $$ Forecaster Brennan

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