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Tropical Storm Laura Forecast Discussion Number 22
2020-08-25 10:59:00| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Tue Aug 25 2020 000 WTNT43 KNHC 250858 TCDAT3 Tropical Storm Laura Discussion Number 22 NWS National Hurricane Center Miami FL AL132020 400 AM CDT Tue Aug 25 2020 Satellite images show that Laura is becoming better organized. Now that the center is clear from Cuba, very deep convection has developed into a ragged, pulsing central dense overcast, with a large curved band on the southern side of the circulation. The intensity is kept at 55 kt, matching the satellite estimates and a blend of the earlier flight-level and SFMR reconnaissance data. Hurricane Hunter missions from both the Air Force and NOAA should be in the storm within a couple hours to help obtain a new estimate. After a westward jog earlier, Laura is estimated to be moving west-northwestward again or 290/15. The synoptic situation consists over a large ridge near the southeastern United States and a weakness in the ridge over Central Texas due to an inverted trough. Laura should gradually gain latitude and turn to the northwest and north-northwest over the next two days while it is steered between those two features, move northward late this week through the southern United States, then move quickly eastward across the eastern U.S. over the weekend as it encounters the mid-latitude westerlies. The majority of the guidance has shifted a notable distance to the west on this run, perhaps due to a weaker trough over Texas and a more westward initial position of Laura (possibly due to persistent northerly mid-level shear). The new NHC prediction is at the eastern edge of the new guidance envelope since I don't want to bite off on such a large change on just one set of model runs. But since the storm has been tracking west of forecast expectations for quite some time, future westward track adjustments could be required later today. Laura is forecast to move over the very warm and deep waters of the Gulf of Mexico, with similar or lighter shear conditions through the next couple of days. Now that an inner core appears to be trying to form, conditions appear ripe for at least steady intensification, and rapid intensification is becoming more likely before landfall. In fact, almost all of the explicit guidance models, save the statistical-dynamical models, are showing a period of rapid strengthening at some point during the next couple of days. Thus, the new NHC forecast is higher than the last one, but not as high as the most of the regional hurricane models since shear could increase just before landfall. Users are again reminded not to focus on the exact details of the track or intensity forecasts as the average NHC track error at 48 h is around 80 miles and the average intensity error is close to 15 mph. In addition, wind, storm surge, and rainfall hazards will extend far from the center. Key Messages: 1. Laura is forecast to reach the northwestern Gulf Coast as a hurricane late Wednesday and early Thursday. Do not focus on the details of the official forecast given the typical uncertainty in NHC's 2-to-3 day track and intensity predictions. In addition, storm surge, wind, and rainfall hazards will extend well away from Laura's center along the Gulf Coast. 2. There is a risk of life-threatening storm surge from San Luis Pass, Texas, to Ocean Springs, Mississippi, within the next 48 hours, and a storm surge watch is in effect for these areas outside of the southeast Louisiana Hurricane and Storm Damage Risk Reduction System. Residents in these areas should follow any advice given by local officials. 3. Hurricane conditions are possible by late Wednesday from San Luis Pass, Texas, to west of Morgan City, Louisiana, with tropical storm conditions possible by Wednesday afternoon, and a hurricane watch is in effect. Hurricane Warnings will likely be issued for a portion of that area later today. 4. The threat of widespread flash and urban flooding, along with small streams overflowing their banks, will be increasing Wednesday night into Thursday from far eastern Texas, across Louisiana, and Arkansas. This will also lead to minor-to-isolated moderate river flooding. The heavy rainfall threat will spread northeastward into the middle-Mississippi, lower Ohio and Tennessee Valleys Friday and Saturday. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 22.9N 85.7W 55 KT 65 MPH 12H 25/1800Z 23.8N 87.9W 65 KT 75 MPH 24H 26/0600Z 25.1N 90.6W 80 KT 90 MPH 36H 26/1800Z 26.8N 92.7W 95 KT 110 MPH 48H 27/0600Z 29.3N 93.7W 100 KT 115 MPH 60H 27/1800Z 32.1N 93.7W 55 KT 65 MPH...INLAND 72H 28/0600Z 34.5N 93.0W 30 KT 35 MPH...INLAND 96H 29/0600Z 37.0N 86.5W 25 KT 30 MPH...INLAND 120H 30/0600Z 39.0N 73.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Blake
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