| I like to pay attention to word choice in NHC discussions. 10pm CDT Wednesday: "When the system moves into the northern Gulf, a decrease in oceanic heat content, drier mid-tropospheric air, and increased vertical shear should cause at least slow weakening." 4am CDT Thursday: "Just prior to making landfall, the cyclone is forecast to level off in strength or weaken slightly as it moves over the cooler shelf waters and into somewhat less favorable atmospheric conditions." I would consider the earlier sentence to indicate that weakening was a little more likely before landfall than the most recent discussion. It should be noted though that it was written by different forecasters so that might be all it is. Hurricane Delta Discussion Number 15 NWS National Hurricane Center Miami FL AL262020 400 AM CDT Thu Oct 08 2020 Satellite images indicate that Delta remains a well organized hurricane with a central dense overcast feature and curved bands beyond that. There is still no indication of an eye, however, in geostationary satellite images. The Air Force Hurricane Hunters were in Delta a few hours ago and toward the end of that mission, they reported maximum flight-level winds of 102 kt and SFMR winds of 77 kt. Based on a blend of this data, the initial intensity was increased to 85 kt at 0600 UTC. Since the cyclone appears to be generally steady in strength since that time, the wind speed is held at that value. Both the NOAA and Air Force Hurricane Hunters will be investigating Delta later today, and that data will help us assess its strength and structure. The track forecast reasoning is unchanged. Delta is currently moving northwestward at 13 kt on the southwestern periphery of an Atlantic subtropical ridge. The western portion of the ridge is expected to weaken later today as a trough moves eastward across the south-central United States. This change in the steering pattern should cause Delta to turn northward by late tonight and north-northeastward by Friday night. This motion should take the core of the hurricane to the Louisiana coast in a little more than 36 hours (sometime Friday afternoon or evening). After landfall, a turn to the northeast is forecast as a larger trough approaches Delta from the west. The models are in very good agreement, and the NHC track forecast is just an update of the previous one. Delta is expected to continue gradually strengthening during the next 24 hours while it remains over warm deep waters and in an environment of low wind shear and a high amount of moisture. Based on these favorable environmental conditions and the trend in the models, Delta is forecast to regain major hurricane status by tonight. Just prior to making landfall, the cyclone is forecast to level off in strength or weaken slightly as it moves over the cooler shelf waters and into somewhat less favorable atmospheric conditions. Rapid weakening is forecast after Delta moves inland. The intensity models are in fairly good agreement, and the NHC intensity forecast lies near the middle of the guidance envelope. It should be noted that the NHC 1-2 day intensity forecasts are subject to errors of around 1 Saffir-Simpson category. The aircraft and fairly recent scatterometer data indicate that Delta is gradually growing in size. This trend is expected to continue as Delta approaches the Louisiana coast. The NHC wind radii forecast follows a consensus of the global and hurricane regional models. Key Messages: 1. Delta is expected to grow in size as it approaches the northern Gulf Coast, where life-threatening storm surge and dangerous hurricane-force winds are likely beginning Friday, particularly for portions of the Louisiana coast. Storm Surge and Hurricane Warnings are in effect, and residents in these areas should follow advice given by local officials and rush preparedness actions to completion. 2. Significant flash, urban, small stream and minor to isolated moderate river flooding is likely Friday and Saturday from portions of the central Gulf Coast into portions of the Lower Mississippi Valley. As Delta moves farther inland, heavy rainfall is expected in the Ohio Valley and Mid-Atlantic this weekend. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 23.4N 91.8W 85 KT 100 MPH 12H 08/1800Z 24.6N 93.0W 95 KT 110 MPH 24H 09/0600Z 26.4N 93.7W 100 KT 115 MPH 36H 09/1800Z 28.8N 93.4W 90 KT 105 MPH 48H 10/0600Z 31.3N 92.4W 55 KT 65 MPH...INLAND 60H 10/1800Z 33.3N 90.9W 30 KT 35 MPH...INLAND 72H 11/0600Z 34.6N 89.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 12/0600Z...DISSIPATED $$ Forecaster Cangialosi Hurricane Delta Advisory Number 15 NWS National Hurricane Center Miami FL AL262020 400 AM CDT Thu Oct 08 2020 ...DELTA MOVING NORTHWESTWARD OVER THE GULF OF MEXICO... ...HURRICANE CONDITIONS AND LIFE-THREATENING STORM SURGE EXPECTED TO BEGIN ALONG PORTIONS OF THE NORTHERN GULF COAST ON FRIDAY... SUMMARY OF 400 AM CDT...0900 UTC...INFORMATION ---------------------------------------------- LOCATION...23.4N 91.8W ABOUT 450 MI...725 KM SSE OF CAMERON LOUISIANA MAXIMUM SUSTAINED WINDS...100 MPH...155 KM/H PRESENT MOVEMENT...NW OR 305 DEGREES AT 15 MPH...24 KM/H MINIMUM CENTRAL PRESSURE...973 MB...28.74 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: None. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Storm Surge Warning is in effect for... * Sabine Pass to Ocean Springs, Mississippi including Calcasieu Lake, Vermilion Bay, Lake Pontchartrain, Lake Maurepas, and Lake Borgne A Storm Surge Watch is in effect for... * High Island, TX to Sabine Pass * East of Ocean Springs, Mississippi to the Mississippi/Alabama border A Hurricane Warning is in effect for... * East of Sabine Pass to Morgan City, Louisiana A Tropical Storm Warning is in effect for... * San Luis Pass, Texas to Sabine Pass * East of Morgan City, Louisiana to the mouth of the Pearl River, including New Orleans * Lake Pontchartrain and Lake Maurepas A Tropical Storm Watch is in effect for... * East of the mouth of the Pearl River to Bay St. Louis Mississippi A Storm Surge Warning means there is a danger of life-threatening inundation, from rising water moving inland from the coastline, during the next 36 hours in the indicated locations. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov. This is a life-threatening situation. Persons located within these areas should take all necessary actions to protect life and property from rising water and the potential for other dangerous conditions. Promptly follow evacuation and other instructions from local officials. 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 Warning means that hurricane conditions are expected somewhere within the warning area. A warning is typically issued 36 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous. Preparations to protect life and property should be rushed to completion. 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. For storm information specific to your area, please monitor products issued by your national meteorological service. DISCUSSION AND OUTLOOK ---------------------- At 400 AM CDT (0900 UTC), the center of Hurricane Delta was located near latitude 23.4 North, longitude 91.8 West. Delta is moving toward the northwest near 15 mph (24 km/h), and this motion with a a reduction in forward speed is expected today. A turn to the north is forecast to occur by late tonight, followed by a north- northeastward motion by Friday night. On the forecast track, the center of Delta will move over the central Gulf of Mexico today, and move inland within the hurricane warning area Friday afternoon or Friday night. Maximum sustained winds are near 100 mph (155 km/h) with higher gusts. Strengthening is forecast, and Delta is expected to become a major hurricane again by tonight. Some weakening is forecast when Delta approaches the northern Gulf coast on Friday. Hurricane-force winds extend outward up to 35 miles (55 km) from the center and tropical-storm-force winds extend outward up to 125 miles (205 km). The estimated minimum central pressure is 973 mb (28.74 inches). HAZARDS AFFECTING LAND ---------------------- Key messages for Delta can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT1, WMO header WTNT41 KNHC, and on the web at www.hurricanes.gov/text/MIATCDAT1.shtml. 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... Pecan Island to Port Fourchon, LA including Vermilion Bay...7-11 ft Cameron, LA to Pecan Island, LA...4-7 ft Port Fourchon, LA to the Mouth of the Mississippi River...4-6 ft Mouth of the Mississippi River to Ocean Springs, MS...3-5 ft Lake Borgne, Lake Pontchartrain, and Lake Maurepas...3-5 ft Ocean Springs, MS to MS/AL border...2-4 ft High Island, TX to Cameron, LA including Calcasieu Lake...2-4 ft MS/AL border to the AL/FL border including Mobile Bay...1-3 ft Sabine Lake...1-3 ft Port O'Connor, TX to High Island, TX including Galveston Bay...1-3 ft The deepest water will occur along the immediate coast near and to the east of the landfall location, where the surge will be accompanied by large and dangerous 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. WIND: Hurricane conditions are expected within the hurricane warning area by Friday afternoon or evening, with tropical storm conditions expected within this area earlier on Friday. Tropical storm conditions are expected within the tropical storm warning areas on Friday. RAINFALL: Friday through Saturday, Delta is expected to produce 5 to 10 inches of rain, with isolated maximum totals of 15 inches, for southwest into south central Louisiana. These rainfall amounts will lead to significant flash, urban, small stream flooding, along with minor to isolated moderate river flooding. For extreme east Texas into northern Louisiana, southern Arkansas and western Mississippi, Delta is expected to produce 3 to 6 inches of rain, with isolated maximum totals of 10 inches. These rainfall amounts will lead to flash, urban, small stream and isolated minor river flooding. As Delta moves farther inland, 1 to 3 inches of rain, with locally higher amounts, is expected in the Ohio Valley and Mid Atlantic this weekend. TORNADOES: A few tornadoes are possible late tonight through Friday over southern parts of Louisiana and Mississippi SURF: Swells from Delta will begin to affect portions of the northern and western Gulf coast later today. 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 Cangialosi |