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Tropical Storm Iselle Forecast Discussion Number 3
2020-08-27 04:58:36| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Wed Aug 26 2020 000 WTPZ44 KNHC 270258 TCDEP4 Tropical Storm Iselle Discussion Number 3 NWS National Hurricane Center Miami FL EP142020 800 PM PDT Wed Aug 26 2020 Satellite imagery indicates that a convective burst has formed a little closer to the center of Iselle during the past few hours, although the circulation remains at least somewhat elongated. Various subjective and objective satellite intensity estimates are near 35 kt, so that remains the initial intensity. The imagery, as well as model analyses, show that Iselle continues to be undergoing strong easterly shear. Iselle is embedded in a large monsoon gyre, and the southwesterly flow on the south side of the gyre should be the main steering influence for the next 60 h or so. This should result in the cyclone continuing its current slow motion toward the northeast. After that time, the cyclone should separate from the gyre, allowing a mid-level ridge to the north and northeast of the system to become the dominant steering mechanism. This should cause Iselle to turn to the north, then northwest, then eventually to the west. The track guidance is in good agreement with the general scenario, although there is some spread on when and where there turns will occur. The new forecast track is close to the HCCA corrected consensus mode and has only minor adjustments from the previous forecast. Present indications are that the current strong shear will persist for several days, and after 72 h the forecast track takes the cyclone over cooler sea surface temperatures. Based on this, significant strengthening appears unlikely, although short-lived spin ups due to convective bursts are possible. The new intensity forecast is unchanged from the previous forecast in showing little change of strength for 72 h, followed by weakening to a depression and a remnant low. An alternative scenario is that the shear causes Iselle to weaken to a trough at any time during the next 120 h. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 16.2N 116.2W 35 KT 40 MPH 12H 27/1200Z 16.7N 115.8W 35 KT 40 MPH 24H 28/0000Z 17.3N 115.3W 35 KT 40 MPH 36H 28/1200Z 17.9N 114.7W 35 KT 40 MPH 48H 29/0000Z 18.6N 114.1W 35 KT 40 MPH 60H 29/1200Z 19.4N 113.6W 35 KT 40 MPH 72H 30/0000Z 20.7N 113.7W 30 KT 35 MPH 96H 31/0000Z 22.5N 115.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 01/0000Z 22.5N 116.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven
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Hurricane Laura Forecast Discussion Number 29
2020-08-27 04:56:04| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Wed Aug 26 2020 000 WTNT43 KNHC 270255 TCDAT3 Hurricane Laura Discussion Number 29 NWS National Hurricane Center Miami FL AL132020 1000 PM CDT Wed Aug 26 2020 Extremely dangerous Laura has the signature of a classic hurricane on satellite images, with a well-defined eye surrounded by very deep convection. There is little evidence of shear, and the upper-level outflow pattern is extremely well defined, while the cyclone is over sea surface temperatures near 30 deg C. Observations from both NOAA and Air Force Hurricane Hunter aircraft show that Laura continued to strengthen during the evening. Using a blend of adjusted flight-level and SFMR-observed surface winds, the intensity estimate is 130 kt for this advisory. Since there is now little time remaining for the system over water, no significant change in intensity is anticipated until the center crosses the coastline. Laura will weaken rapidly after it begins to move over land, but destructive winds should spread well inland, more than 100 miles, along its path. Later in the forecast period, the ECMWF and U.K. Met. Office global models indicate some baroclinic re-intensification as the remnants of Laura move off the U.S. East coast, and this is reflected in the NHC forecast. Laura has begun to turn northward as it moves around the western side of a subtropical high pressure area, and the initial motion is about 340/13 kt. The track forecast is essentially unchanged from the previous advisories. The cyclone should move through a weakness in the ridge and turn to the northeast over the next day or two. Then the system should accelerate toward the east-northeast while embedded in the westerlies. The official track forecast remains close to both the simple and the corrected dynamical model consensus predictions, TVCA and HCCA. Laura is a large hurricane, and users are reminded to not focus on the precise track forecast since wind, storm surge, and rainfall hazards extend far from the center. Key Messages: 1. Unsurvivable storm surge with large and destructive waves will cause catastrophic damage from Sea Rim State Park, Texas, to Intracoastal City, Louisiana, including Calcasieu and Sabine Lakes. This surge could penetrate up to 40 miles inland from the immediate coastline, and flood waters will not fully recede for several days after the storm. 2. Hurricane-force winds are expected tonight in portions of the hurricane warning area, with catastrophic wind damage expected where Laura's eyewall moves onshore. Hurricane-force winds and widespread damaging wind gusts will spread well inland into portions of extreme eastern Texas and western Louisiana early Thursday. 3. Widespread flash flooding along small streams, urban areas, and roadways is expected to begin overnight tonight into Thursday from far eastern Texas into Louisiana and Arkansas. This will also lead to minor to moderate freshwater river flooding. The heavy rainfall threat and flash and urban flooding potential will spread northeastward into the middle-Mississippi, lower Ohio, and Tennessee Valleys Friday night and Saturday. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 29.0N 93.2W 130 KT 150 MPH 12H 27/1200Z 31.0N 93.7W 95 KT 110 MPH...INLAND 24H 28/0000Z 33.8N 92.9W 50 KT 60 MPH...INLAND 36H 28/1200Z 35.6N 91.5W 35 KT 40 MPH...INLAND 48H 29/0000Z 36.8N 88.2W 25 KT 30 MPH...INLAND 60H 29/1200Z 37.5N 82.7W 25 KT 30 MPH...POST-TROP/INLAND 72H 30/0000Z 38.5N 75.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 31/0000Z 45.0N 60.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 01/0000Z 52.0N 46.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch
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Hurricane Laura Forecast Discussion Number 28
2020-08-26 22:51:32| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Wed Aug 26 2020 000 WTNT43 KNHC 262051 TCDAT3 Hurricane Laura Discussion Number 28 NWS National Hurricane Center Miami FL AL132020 400 PM CDT Wed Aug 26 2020 Laura has continued to rapidly strengthen today with recent visible satellite imagery revealing a very distinct 25 nautical- mile-wide eye embedded in a symmetric central dense overcast. The upper-level outflow has also become well established in all quadrants. An Air Force Reserve hurricane hunter aircraft that is still investigating the hurricane has reported peak 700-mb flight-level winds of 136 kt and SFMR winds of 121 kt in the northeast eyewall. These data support an initial intensity of 125 kt, which is an increase of 55 kt over the past 24 hours. The minimum pressure has fallen to around 947 mb. The well-defined eye is now within range of the NWS Lake Charles WSR-88D radar, and hourly Tropical Cyclone Updates began at 1900 UTC (2 PM CDT) and will continue through landfall and beyond overnight. Laura still has about 12 hours remaining over the warm waters of the northwest Gulf of Mexico waters, but increasing southwesterly shear around the time of landfall and the possibility of an eyewall replacement could result in some fluctuations in intensity this evening, but Laura is expected to remain an extremely dangerous category 4 hurricane through landfall tonight. Although rapid weakening is expected on Thursday as Laura moves inland, the hurricane is expected to bring a swath of damaging winds well inland over western Louisiana and extreme eastern Texas. The cyclone or its remnants are forecast to move off Mid-Atlantic coast over the weekend and there remains some possibility that Laura will re-intensify as a tropical cyclone offshore of the United States east before it merges with a frontal boundary later in the forecast period. Recent satellite and aircraft fixes show that Laura is moving northwestward at about 13 kt. Laura is nearing the western extent of a mid-level ridge that is located over the southeastern United States. The hurricane should turn north-northwestward this evening and northward on Thursday between the ridge and a weak trough over the south-central United States. By Friday the cyclone should turn northeastward and then east-northeastward as it becomes embedded in the mid-latitude westerlies. The track model guidance continues to be in good agreement through 72, but there are some forward speed differences thereafter. The new NHC track is very close to the previous advisory and is near the middle of the guidance envelope. Laura is a large hurricane and users are reminded to not focus on the precise track forecast since wind, storm surge, and rainfall hazards extend far from the center. Key Messages: 1. Unsurvivable storm surge with large and destructive waves will cause catastrophic damage from Sea Rim State Park, Texas, to Intracoastal City, Louisiana, including Calcasieu and Sabine Lakes. This surge could penetrate up to 40 miles inland from the immediate coastline, and flood waters will not fully recede for several days after the storm. 2. Hurricane-force winds are expected tonight in portions of the hurricane warning area, with catastrophic wind damage expected where Laura's eyewall moves onshore. Hurricane-force winds and widespread damaging wind gusts will spread well inland into portions of extreme eastern Texas and western Louisiana early Thursday. 3. Widespread flash flooding along small streams, urban areas, and roadways is expected to begin this afternoon into Thursday from far eastern Texas into Louisiana and Arkansas. This will also lead to minor to moderate freshwater river flooding. The heavy rainfall threat and flash and urban flooding potential will spread northeastward into the middle-Mississippi, lower Ohio, and Tennessee Valleys Friday night and Saturday. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 27.9N 92.8W 125 KT 145 MPH 12H 27/0600Z 29.7N 93.6W 130 KT 150 MPH 24H 27/1800Z 32.5N 93.5W 60 KT 70 MPH...INLAND 36H 28/0600Z 34.8N 92.7W 35 KT 40 MPH...INLAND 48H 28/1800Z 36.5N 90.1W 25 KT 30 MPH...INLAND 60H 29/0600Z 37.3N 85.6W 25 KT 30 MPH...INLAND 72H 29/1800Z 38.0N 79.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 30/1800Z 43.2N 64.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 31/1800Z 51.0N 49.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown
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Hurricane Laura Forecast Discussion Number 27
2020-08-26 17:15:56| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Wed Aug 26 2020 000 WTNT43 KNHC 261515 CCA TCDAT3 Hurricane Laura Discussion Number 27...Corrected NWS National Hurricane Center Miami FL AL132020 1000 AM CDT Wed Aug 26 2020 Corrected 24-h status in forecast table to inland. Laura has become a very powerful hurricane this morning. The satellite presentation has continued to improve with the eye becoming better defined, and cloud tops colder than -70C in the surrounding ring of deep convection. Both NOAA and Air Force hurricane hunter aircraft have provided valuable data this morning. The NOAA P-3 aircraft reported a peak flight-level wind of 125 kt at 8000 ft, and a peak SFMR wind of 104 kt, while the Air Force crew has observed peak 700-mb flight-level winds of 121 kt and peak SFMR winds of 104 kt. The lastest minimum pressure estimated from aircraft data is 956 mb, indicating a pressure drop of 27 mb over the past 12 hours. Based on the aircraft data, the initial wind speed was increased to 100 kt on the 1200 UTC intermediate advisory, and is now set at 110 kt based on the latest flight-level and SFMR winds. Laura is likely to continue strengthening today while it moves over warm waters of the northwestern Gulf of Mexico and the vertical wind shear remains low. Laura's intensity could level-off by this evening due to the possibility of an eyewall replacement cycle and the expected increase in shear around the time of landfall. Even if the rate of strengthening eases, Laura is expected to be an extremely powerful category 4 hurricane when it reaches the northwestern Gulf coast. After landfall, rapid weakening will occur, but Laura will bring a swath of damaging winds well inland over western Louisiana and eastern Texas. The UKMET and ECMWF models suggest that there is some chance that Laura re-intensifies as a tropical cyclone off the mid-Atlantic coast, but given the uncertainties at that time range the forecast continues to show it as a post-tropical cyclone at days 4 and 5. Laura is moving northwestward at about 13 kt. A gradual turn toward the north-northwest and north are expected within the next 12-18 hours as the hurricane moves around the western portion of a mid- level ridge that extends from the western Atlantic into the southeastern United States. This motion will bring the center of Laura onshore in southwestern Louisiana or extreme eastern Texas tonight. By Thursday night, Laura is forecast to turn northeastward, and then east-northeastward on Friday as it becomes embedded in the mid-latitude westerlies. The dynamical track models are in good agreement, and little adjustment to the previous NHC forecast track was required. Laura is a large hurricane and users are reminded to not focus on the precise track forecast since wind, storm surge, and rainfall hazards extend far from the center. Key Messages: 1. Unsurvivable storm surge with large and destructive waves will cause catastrophic damage from Sea Rim State Park, Texas, to Intracoastal City, Louisiana, including Calcasieu and Sabine Lakes. This surge could penetrate up to 30 miles inland from the immediate coastline. Only a few hours remain to protect life and property and all actions should be rushed to completion. 2. Hurricane-force winds are expected tonight in portions of the hurricane warning area from San Luis Pass, Texas, to west of Morgan City, Louisiana, with catastrophic wind damage expected where Laura's eyewall makes landfall. Hurricane-force winds and widespread damaging wind gusts will spread well inland across portions of eastern Texas and western Louisiana early Thursday. 3. Widespread flash flooding along small streams, urban areas, and roadways is expected to begin this afternoon into Thursday from far eastern Texas, across Louisiana and Arkansas. This will also lead to minor to isolated moderate freshwater river flooding. The heavy rainfall threat and localized flash and urban flooding potential will spread northeastward into the middle-Mississippi, lower Ohio and Tennessee Valleys Friday night and Saturday. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 27.0N 92.0W 110 KT 125 MPH 12H 27/0000Z 28.5N 93.2W 125 KT 145 MPH 24H 27/1200Z 31.0N 93.8W 75 KT 85 MPH...INLAND 36H 28/0000Z 33.7N 93.5W 40 KT 45 MPH...INLAND 48H 28/1200Z 35.8N 92.2W 25 KT 30 MPH...INLAND 60H 29/0000Z 37.2N 89.1W 25 KT 30 MPH...INLAND 72H 29/1200Z 37.6N 83.9W 25 KT 30 MPH...INLAND 96H 30/1200Z 40.0N 70.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 31/1200Z 48.0N 55.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown
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Tropical Depression Thirteen-E Forecast Discussion Number 2
2020-08-26 16:55:23| National Hurricane Center (East Pacific)
Issued at 900 AM MDT Wed Aug 26 2020 000 WTPZ43 KNHC 261454 CCA TCDEP3 Tropical Depression Thirteen-E Discussion Number 2 NWS National Hurricane Center Miami FL EP132020 900 AM MDT Wed Aug 26 2020 CORRECTED ADVISORY NUMBER The depression remains poorly organized this morning with the ill-defined surface circulation decoupled well to the east of the convective mass. Subjective satellite intensity estimates from both TAFB and SAB support 30 kt for this advisory. UW-CIMSS shear analysis product shows stiff 20-25 kt of east-northeasterly shear impinging on the east portion of the depression. Both the FV3/GFS and ECMWF SHIPS statistical-dynamical intensity models indicate that the strong shear will persist through the forecast period. Consequently, little strengthening is expected during the next several days. Because of the vertical direction and magnitude, the forecast tropical-storm-force winds and the heaviest rainfall should remain offshore of the southwestern coast of Mexico. The NHC intensity forecast follows a blend of the multi-model intensity guidance, and the global models beyond the 48 hr period which indicate the depression degenerating into a remnant low on day 3, and dissipation by day 5. The initial motion is estimated to be a drift east-northeastward, or 065/2 kt. The cyclone is embedded within an northeast-to-southwest oriented cyclonic gyre, similar to a reverse monsoon trough that typically forms in the western Pacific during the summer months. The depression is forecast to drift today in a general east-northeast to northeast direction followed by a turn slowly north-northeastward tonight. A motion toward the north-northwest is expected on Thursday. Afterward, a mid-tropospheric ridge anchored over the southwestern U.S. should force the cyclone west-northwestward to westward on Friday and Saturday. On the forecast track, the depression should remain just offshore the southwestern coast of Mexico today and Thursday, and pass near or just south of the southern tip of Baja California Sur on Friday and Saturday. The official track forecast is basically an update of the previous advisory and is nudged toward the NOAA HFIP Corrected Consensus model. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 17.3N 106.1W 30 KT 35 MPH 12H 27/0000Z 18.1N 106.1W 30 KT 35 MPH 24H 27/1200Z 19.0N 106.3W 35 KT 40 MPH 36H 28/0000Z 20.4N 107.2W 35 KT 40 MPH 48H 28/1200Z 21.4N 108.5W 30 KT 35 MPH 60H 29/0000Z 22.2N 110.1W 30 KT 35 MPH 72H 29/1200Z 22.6N 112.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 30/1200Z 22.6N 114.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 31/1200Z...DISSIPATED $$ Forecaster Roberts
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