| Track: https://www.nhc.noaa.gov/refresh/graphics_at3+shtml/?cone#contents 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 Tropical Storm Laura Advisory Number 22 NWS National Hurricane Center Miami FL AL132020 400 AM CDT Tue Aug 25 2020 ...LAURA NOW FORECAST TO BECOME A MAJOR HURRICANE OVER THE NORTHWESTERN GULF OF MEXICO ON WEDNESDAY... ...ADDITIONAL HURRICANE WATCH AREA ISSUED FOR PORTIONS OF TEXAS... SUMMARY OF 400 AM CDT...0900 UTC...INFORMATION ---------------------------------------------- LOCATION...22.9N 85.7W ABOUT 85 MI...140 KM NW OF THE WESTERN TIP OF CUBA ABOUT 680 MI...1095 KM SE OF LAKE CHARLES LOUISIANA MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H PRESENT MOVEMENT...WNW OR 290 DEGREES AT 17 MPH...28 KM/H MINIMUM CENTRAL PRESSURE...995 MB...29.39 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: The Tropical Storm Watch from South of Port Bolivar to San Luis Pass has been changed to a Hurricane Watch. A Tropical Storm Watch has been issued from San Luis Pass to Freeport Texas. The Tropical Storm Warning for the Florida Keys from the Seven Mile Bridge to Key West has been discontinued. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Storm Surge Watch is in effect for... * San Luis Pass Texas to Ocean Springs Mississippi * Lake Pontchartrain, Lake Maurepas, and Lake Borgne A Hurricane Watch is in effect for... * San Luis Pass Texas to west of Morgan City Louisiana A Tropical Storm Warning is in effect for... * Cuban provinces of Villa Clara, Cienfuegos, Matanzas, Mayabeque, La Habana, Artemisa, Pinar del Rio, and the Isle of Youth * Dry Tortugas A Tropical Storm Watch is in effect for... * San Luis Pass to Freeport Texas * Morgan City Louisiana to the Mouth of the Mississippi River A Storm Surge Watch means there is a possibility of life- threatening inundation, from rising water moving inland from the coastline, in the indicated locations during the next 48 hours. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov. A Hurricane Watch means that hurricane conditions are possible within the watch area. A watch is typically issued 48 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous. A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area. A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours. Hurricane Warnings will likely to issued later this morning or afternoon for portions of the Texas and Louisiana coasts. For storm information specific to your area in the United States, including possible inland watches and warnings, please monitor products issued by your local National Weather Service forecast office. For storm information specific to your area outside of the United States, please monitor products issued by your national meteorological service. DISCUSSION AND OUTLOOK ---------------------- At 400 AM CDT (0900 UTC), the center of Tropical Storm Laura was located near latitude 22.9 North, longitude 85.7 West. Laura is moving toward the west-northwest near 17 mph (28 km/h). This general motion should continue today. A turn toward the northwest is forecast by Wednesday, and a northwestward to north-northwestward motion should continue through Wednesday night. On the forecast track, the center of Laura will move away from Cuba and over the southeastern Gulf of Mexico this morning. Laura is then forecast to move over the central and northwestern Gulf of Mexico tonight and Wednesday, approach the Upper Texas and Southwest Louisiana coasts on Wednesday night and move inland near those area on Thursday. Maximum sustained winds remain 65 mph (100 km/h) with higher gusts. Significant strengthening is forecast during the next 48 hours, and Laura is now expected to be a major hurricane at landfall. Tropical-storm-force winds extend outward up to 175 miles (280 km) from the center. The estimated minimum central pressure is 995 mb (29.39 inches). HAZARDS AFFECTING LAND ---------------------- Key messages for Laura can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT3 and WMO header WTNT43 KNHC. STORM SURGE: The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline. The water could reach the following heights above ground somewhere in the indicated areas if the peak surge occurs at the time of high tide... High Island TX to Morgan City LA including Sabine Lake, Calcasieu Lake, and Vermilion Bay...7-11 ft Port Bolivar TX to High Island TX...4-6 ft Morgan City LA to Mouth of the Mississippi River...4-6 ft Mouth of the Mississippi River to Ocean Springs MS including Lake Borgne...3-5 ft San Luis Pass TX to Port Bolivar TX...2-4 ft Galveston Bay...2-4 ft Lake Pontchartrain and Lake Maurepas...2-4 ft The deepest water will occur along the immediate coast near and to the right of the landfall location, where the surge will be accompanied by large and destructive waves. Surge-related flooding depends on the relative timing of the surge and the tidal cycle, and can vary greatly over short distances. For information specific to your area, please see products issued by your local National Weather Service forecast office. RAINFALL: Laura is expected to produce the following storm total rainfall accumulations: Rainfall will be coming to an end across western Cuba Tuesday morning with additional rainfall totals of 1 to 2 inches possible. From Wednesday afternoon into Saturday, Laura is expected to produce rainfall of 4 to 8 inches, with isolated maximum amounts of 12 inches across portions of the west-central U.S. Gulf Coast near the Texas and Louisiana border north into portions of the lower Mississippi Valley. This rainfall could cause widespread flash and urban flooding, small streams to overflow their banks, and minor to isolated moderate river flooding. WIND: Tropical storm conditions are expected to spread westward within the warning area in western Cuba during the next few hours. Tropical storm conditions are also expected for the Dry Tortugas for a few more hours. Hurricane conditions are possible in the hurricane watch area along the Gulf Coast by late Wednesday, with tropical storm conditions possible by Wednesday afternoon. SURF: Swells generated by Laura are affecting portions of Cuba, the central Bahamas, and the Florida Keys. Swells are expected to spread northward along portions of the west coast of Florida peninsula and the coast of the Florida panhandle later today and tonight, and reach the northern and northwest Gulf coast by Wednesday. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office. NEXT ADVISORY ------------- Next intermediate advisory at 700 AM CDT. Next complete advisory at 1000 AM CDT. $$ Forecaster Blake |