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Hurricane Laura Forecast Discussion Number 24
2020-08-25 22:40:45| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Tue Aug 25 2020 000 WTNT43 KNHC 252040 TCDAT3 Hurricane Laura Discussion Number 24 NWS National Hurricane Center Miami FL AL132020 400 PM CDT Tue Aug 25 2020 Satellite imagery shows some changes in the convective pattern of Laura since the last advisory. The ragged central dense overcast seen earlier has been replaced by a curved convective band that wraps almost all the way around a cloud-filled banding-type eve. One possible reason for this change is that the imagery also suggests a tongue of dry air is trying to entrain into the cyclone just west of the central convection. Aircraft data received after the last advisory did not show any fall in the central pressure, but did have high enough flight-level and SFMR winds to justify nudging the initial intensity up to 70 kt. The initial motion is now west-northwestward or 300/15 kt. There is no change in the forecast philosophy since the last advisory. The hurricane is currently on the south side of a large-deep layer ridge over the southeastern United States, and it is moving toward a break in the ridge caused by mid- to -upper-level troughing over Texas and the southern Great Plains. The current and forecast synoptic pattern should steer Laura west-northwestward this evening, followed by a turn toward the northwest tonight and toward the north by Wednesday night and Thursday. This will result in the hurricane making landfall in the area of southwestern Louisiana or the upper Texas coast late Wednesday night or Thursday morning. The new forecast track has a slight eastward nudge during the first 12-24 h, but the landfall position is almost unchanged from that of the previous forecast. It should the be noted that the current forecast track lies to the east of the ECMWF and UKMET models, so it is still possible that the forecast track could nudge westward in later advisories. After landfall, Laura is expected to recurve into the westerlies and move eastward through the Tennessee Valley and the mid-Atlantic States before reaching the Atlantic in about 120 h. All indications are that the hurricane should steadily to rapidly intensify during the next 24 h, with the only negative factor being the possibility of more dry air entrainment. The intensity forecast will go with the scenario that the dry air will not significantly hinder strengthening. The global models are in good agreement that Laura will encounter increasing southwesterly shear in the last 6-12 h before landfall, so the intensity forecast shows slower strengthening during that time. With all that said, the landfall intensity of 100 kt is unchanged from the previous advisory. After landfall, Laura should weaken through the 96 h point, followed by re-intensification through baroclinic energy as the cyclone becomes extratropical. Users are again reminded not to focus on the exact details of the track or intensity forecasts as the average NHC track error at 36 h is around 60 miles and the average intensity error is close to 10 mph. In addition, wind, storm surge, and rainfall hazards will extend far from the center. Key Messages: 1. There is a danger of life-threatening storm surge with large and dangerous waves producing potentially catastrophic damage from San Luis Pass, Texas, to the Mouth of the Mississippi River, including areas inside the Port Arthur Hurricane Flood Protection system. This surge could penetrate up to 30 miles inland from the immediate coastline in southwestern Louisiana and far southeastern Texas. Actions to protect life and property should be rushed to completion this evening, as water levels will begin to rise on Wednesday. 2. Hurricane-force winds are expected Wednesday night in the warning area from San Luis Pass, Texas, to west of Morgan City, Louisiana, and the strongest winds associated with Laura's eyewall will occur somewhere within this area. Hurricane-force winds and widespread damaging wind gusts are also expected to spread well inland into portions of eastern Texas and western Louisiana early Thursday. 3. The threat of widespread flash and urban flooding along with small streams overflowing their banks will increase due to heavy rainfall Wednesday night into Thursday from far eastern Texas, across Louisiana, and Arkansas. This will also result in minor to isolated moderate river flooding. The heavy rainfall threat will spread northeastward into the middle-Mississippi, lower Ohio and Tennessee Valleys Friday night and Saturday. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 24.7N 88.3W 70 KT 80 MPH 12H 26/0600Z 25.7N 90.3W 85 KT 100 MPH 24H 26/1800Z 27.5N 92.4W 95 KT 110 MPH 36H 27/0600Z 29.7N 93.8W 100 KT 115 MPH...ON COAST 48H 27/1800Z 32.2N 93.9W 65 KT 75 MPH...INLAND 60H 28/0600Z 34.7N 93.3W 40 KT 45 MPH...INLAND 72H 28/1800Z 36.5N 90.9W 30 KT 35 MPH...INLAND 96H 29/1800Z 38.5N 80.5W 25 KT 30 MPH...INLAND 120H 30/1800Z 42.0N 66.5W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven
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