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Hurricane Ida Forecast Discussion Number 14

2021-08-29 16:56:33| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Sun Aug 29 2021 167 WTNT44 KNHC 291456 TCDAT4 Hurricane Ida Discussion Number 14 NWS National Hurricane Center Miami FL AL092021 1000 AM CDT Sun Aug 29 2021 Ida's rapid strengthening appears to have leveled off within the past hour or so. NOAA and Air Force Reserve Hurricane Hunter aircraft that have been in the storm this morning have reported peak flight-level winds of 146 to 148 kt between 8000 and 10000 ft, and believable SFMR winds around 130 kt. Based on these observations, the initial wind speed remains 130 kt for this advisory. The central pressure appears to have bottomed out around 929 mb, and the latest dropsonde in the eye from the Air Force plane supports a minimum pressure of 933 mb. Ida's satellite and radar presentation is very impressive, as the 15-nm-wide eye is very well-defined and surrounded by a ring of intense convection. Within the past hour or so, there is evidence in radar imagery of a secondary eyewall, and this has likely caused Ida's intensity to level off for now. Although Ida's extreme winds are confined to the inner eyewall, the aircraft data indicate that hurricane-force winds extend outward about 45 n mi to the northeast of the center, and based on buoy data the tropical-storm-force wind field extends outward about 130 n mi northeast of the center. Ida's eyewall is nearing the coast of Louisiana, and any additional strengthening seems less likely now given the recent structural changes of the inner core. While rapid weakening should occur after landfall, damaging winds will penetrate well inland across southeastern Louisiana and southwestern Mississippi through tonight. Ida is forecast to weaken to a tropical depression over Mississippi by late Tuesday. The global model guidance now indicates that Ida will likely transition to an extratropical low when it nears the east coast of the United States and the new forecast shows the extratropical low becoming a gale center near Atlantic Canada at day 5. Ida has begun to slow down according to the latest aircraft and radar fixes, and the initial motion estimate is 320/11 kt. Ida's forward speed is likely to slow further during the next 12 to 24 hours as the hurricane turns north-northwestward, and then northward around the western periphery of a deep-layer ridge near the southeastern United States coast. The cyclone is predicted to turn northeastward by late Tuesday ahead of a short-wave trough that will move across the central United States. The new NHC track is close to the HCCA corrected consensus and the GFS ensemble mean, and is not very different from the previous advisory. Key Messages: 1. Extremely life-threatening storm surge inundation of 9 feet or greater above ground level is imminent somewhere within the area from Burns Point, Louisiana, to Ocean Springs, Mississippi. Overtopping of local levees outside of the Hurricane and Storm Damage Risk Reduction System is possible where local inundation values may be higher. 2. Catastrophic wind damage will occur where the core of Ida moves onshore along the southeast coast of Louisiana in the next few hours. Hurricane-force winds and damaging wind gusts are expected today within the Hurricane Warning in southeastern Louisiana, including metropolitan New Orleans. 3. Damaging winds, especially in gusts, will spread inland near the track of the center of Ida into southwestern Mississippi tonight and early Monday. These winds will likely lead to widespread tree damage and power outages. 4. Ida will continue to produce heavy rainfall today through Monday across the central Gulf Coast from southeast Louisiana, coastal Mississippi, and far southwestern Alabama, resulting in considerable to life-threatening flash and urban flooding and significant river flooding impacts. As Ida moves inland, significant flooding impacts are possible across portions of the Lower Mississippi, Tennessee Valley, Upper Ohio Valley, Central Appalachians and the Mid-Atlantic through Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 28.8N 90.0W 130 KT 150 MPH 12H 30/0000Z 30.0N 90.8W 90 KT 105 MPH...INLAND 24H 30/1200Z 31.6N 91.0W 50 KT 60 MPH...INLAND 36H 31/0000Z 33.2N 90.3W 30 KT 35 MPH...INLAND 48H 31/1200Z 34.9N 88.5W 25 KT 30 MPH...INLAND 60H 01/0000Z 36.4N 85.9W 20 KT 25 MPH...INLAND 72H 01/1200Z 37.8N 82.5W 20 KT 25 MPH...POST-TROP/INLAND 96H 02/1200Z 40.5N 74.2W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 03/1200Z 43.5N 67.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Tropical Storm Julian Forecast Discussion Number 3

2021-08-29 16:53:37| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sun Aug 29 2021 000 WTNT41 KNHC 291453 TCDAT1 Tropical Storm Julian Discussion Number 3 NWS National Hurricane Center Miami FL AL112021 1100 AM AST Sun Aug 29 2021 The system has become better organized this morning, with the low-level center located on the southwestern edge of a persistent mass of deep convection. A 1246 UTC ASCAT-B pass revealed an area of winds over 40 kt southeast of the center, so the system is upgraded to Tropical Storm Julian with maximum winds of 45 kt. Julian is accelerating toward the northeast (045/15 kt) in the flow to the south of a deep-layer area of low pressure located just east of Newfoundland. The storm is expected to move around the southeastern and eastern periphery of this large low during the next few days, accelerating further and turning toward the north by 48 hours. The track models are all in good agreement on this scenario, and the NHC track forecast is very close to the TVCA and HCCA consensus aids. This new forecast is also relatively unchanged from the previous advisory. Winds in the storm have increased faster than expected, even in the face of 20 kt of west-southwesterly shear. This shear is forecast to increase substantially in the coming days, with SHIPS diagnostics indicating it may reach magnitudes of 40-50 kt. However, the storm will still be moving over marginally warm waters around 26 degrees Celsius, and its fast motion and some baroclinic forcing could allow for additional strengthening during the next 12-24 hours. Nearly all the intensity models support some strengthening, and the NHC official forecast peaks the winds at 55 kt in 24 hours, roughly between the IVCN and HCCA solutions. Phase-space diagrams suggest that Julian will probably already be going through extratropical transition at that time, and it should be fully extratropical by 36 hours. Gradual weakening is anticipated after 24 hours, and the extratropical low is likely to dissipate over the north Atlantic by day 3. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 35.1N 46.8W 45 KT 50 MPH 12H 30/0000Z 36.9N 43.7W 50 KT 60 MPH 24H 30/1200Z 40.0N 39.7W 55 KT 65 MPH 36H 31/0000Z 43.6N 37.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 31/1200Z 48.0N 36.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 60H 01/0000Z 52.2N 38.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 01/1200Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Julian Wind Speed Probabilities Number 3

2021-08-29 16:53:37| National Hurricane Center (Atlantic)

Issued at 1500 UTC SUN AUG 29 2021 000 FONT11 KNHC 291453 PWSAT1 TROPICAL STORM JULIAN WIND SPEED PROBABILITIES NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112021 1500 UTC SUN AUG 29 2021 AT 1500Z THE CENTER OF TROPICAL STORM JULIAN WAS LOCATED NEAR LATITUDE 35.1 NORTH...LONGITUDE 46.8 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 45 KTS...50 MPH...85 KM/H. Z INDICATES COORDINATED UNIVERSAL TIME (GREENWICH) ATLANTIC STANDARD TIME (AST)...SUBTRACT 4 HOURS FROM Z TIME EASTERN DAYLIGHT TIME (EDT)...SUBTRACT 4 HOURS FROM Z TIME CENTRAL DAYLIGHT TIME (CDT)...SUBTRACT 5 HOURS FROM Z TIME WIND SPEED PROBABILITY TABLE FOR SPECIFIC LOCATIONS CHANCES OF SUSTAINED (1-MINUTE AVERAGE) WIND SPEEDS OF AT LEAST ...34 KT (39 MPH... 63 KM/H)... ...50 KT (58 MPH... 93 KM/H)... ...64 KT (74 MPH...119 KM/H)... FOR LOCATIONS AND TIME PERIODS DURING THE NEXT 5 DAYS PROBABILITIES FOR LOCATIONS ARE GIVEN AS OP(CP) WHERE OP IS THE PROBABILITY OF THE EVENT BEGINNING DURING AN INDIVIDUAL TIME PERIOD (ONSET PROBABILITY) (CP) IS THE PROBABILITY OF THE EVENT OCCURRING BETWEEN 12Z SUN AND THE FORECAST HOUR (CUMULATIVE PROBABILITY) PROBABILITIES ARE GIVEN IN PERCENT X INDICATES PROBABILITIES LESS THAN 1 PERCENT PROBABILITIES FOR 34 KT AND 50 KT ARE SHOWN AT A GIVEN LOCATION WHEN THE 5-DAY CUMULATIVE PROBABILITY IS AT LEAST 3 PERCENT. PROBABILITIES FOR 34...50...64 KT SHOWN WHEN THE 5-DAY 64-KT CUMULATIVE PROBABILITY IS AT LEAST 1 PERCENT. - - - - WIND SPEED PROBABILITIES FOR SELECTED LOCATIONS - - - - FROM FROM FROM FROM FROM FROM FROM TIME 12Z SUN 00Z MON 12Z MON 00Z TUE 12Z TUE 12Z WED 12Z THU PERIODS TO TO TO TO TO TO TO 00Z MON 12Z MON 00Z TUE 12Z TUE 12Z WED 12Z THU 12Z FRI FORECAST HOUR (12) (24) (36) (48) (72) (96) (120) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - LOCATION KT $$ FORECASTER BERG

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Tropical Storm Julian Public Advisory Number 3

2021-08-29 16:53:06| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sun Aug 29 2021 000 WTNT31 KNHC 291452 TCPAT1 BULLETIN Tropical Storm Julian Advisory Number 3 NWS National Hurricane Center Miami FL AL112021 1100 AM AST Sun Aug 29 2021 ...TROPICAL STORM JULIAN FORMS OVER THE CENTRAL SUBTROPICAL ATLANTIC... ...EXPECTED TO BECOME POST-TROPICAL ON MONDAY... SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION ----------------------------------------------- LOCATION...35.1N 46.8W ABOUT 865 MI...1390 KM SSE OF CAPE RACE NEWFOUNDLAND ABOUT 1115 MI...1795 KM W OF THE AZORES MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H PRESENT MOVEMENT...NE OR 45 DEGREES AT 17 MPH...28 KM/H MINIMUM CENTRAL PRESSURE...998 MB...29.47 INCHES WATCHES AND WARNINGS -------------------- There are no coastal watches or warnings in effect. DISCUSSION AND OUTLOOK ---------------------- At 1100 AM AST (1500 UTC), the center of Tropical Storm Julian was located near latitude 35.1 North, longitude 46.8 West. Julian is moving toward the northeast near 17 mph (28 km/h). A faster motion toward the northeast and then north over the north Atlantic is expected through Tuesday. Satellite-derived wind data indicate that maximum sustained winds have increased to near 50 mph (85 km/h) with higher gusts. Some additional strengthening is anticipated through tonight. Weakening should begin on Monday, with Julian likely becoming post-tropical by Monday evening. Tropical-storm-force winds extend outward up to 90 miles (150 km) from the center. The estimated minimum central pressure is 998 mb (29.47 inches). HAZARDS AFFECTING LAND ---------------------- None. NEXT ADVISORY ------------- Next complete advisory at 500 PM AST. $$ Forecaster Berg

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Hurricane Ida Public Advisory Number 14

2021-08-29 16:53:05| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Sun Aug 29 2021 000 WTNT34 KNHC 291452 TCPAT4 BULLETIN Hurricane Ida Advisory Number 14 NWS National Hurricane Center Miami FL AL092021 1000 AM CDT Sun Aug 29 2021 ...EYE OF EXTREMELY DANGEROUS CATEGORY 4 HURRICANE IDA NEARING THE SOUTHEASTERN COAST OF LOUISIANA... ...CATASTROPHIC STORM SURGE AND HURRICANE-FORCE WINDS MOVING ONSHORE... SUMMARY OF 1000 AM CDT...1500 UTC...INFORMATION ----------------------------------------------- LOCATION...28.8N 90.0W ABOUT 60 MI...95 KM WSW OF THE MOUTH OF THE MISSISSIPPI RIVER ABOUT 85 MI...135 KM S OF NEW ORLEANS LOUISIANA MAXIMUM SUSTAINED WINDS...150 MPH...240 KM/H PRESENT MOVEMENT...NW OR 320 DEGREES AT 13 MPH...20 KM/H MINIMUM CENTRAL PRESSURE...933 MB...27.55 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: The Storm Surge Warning west of Intracoastal City, Louisiana, has been discontinued. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Storm Surge Warning is in effect for... * Intracoastal City Louisiana to the Alabama/Florida border * Vermilion Bay, Lake Borgne, Lake Pontchartrain, Lake Maurepas, and Mobile Bay A Hurricane Warning is in effect for... * Intracoastal City Louisiana to the Mouth of the Pearl River * Lake Pontchartrain, Lake Maurepas, and Metropolitan New Orleans A Tropical Storm Warning is in effect for... * Cameron Louisiana to west of Intracoastal City Louisiana * Mouth of the Pearl River to the Alabama/Florida border A Storm Surge Warning means there is a danger of life-threatening inundation from rising water moving inland from the coastline 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 Hurricane Warning means that hurricane conditions are expected somewhere within the warning area. A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area. For storm information specific to your area, including possible inland watches and warnings, please monitor products issued by your local National Weather Service forecast office. DISCUSSION AND OUTLOOK ---------------------- At 1000 AM CDT (1500 UTC), the eye of Hurricane Ida was located by reconnaissance aircraft and NWS Doppler radar near latitude 28.8 North, longitude 90.0 West. Ida is moving toward the northwest near 13 mph (20 km/h). A slightly slower northwestward motion should continue through this evening. A turn toward the north should occur by Monday morning, followed by a slightly faster northeastward motion by Monday night and Tuesday. On the forecast track, the center of Ida will make landfall along the coast of southeastern Louisiana within the hurricane warning area within the next few hours. Ida is then forecast to move well inland over portions of Louisiana and western Mississippi Monday and Monday night, and move across the Tennessee Valley on Tuesday. Reports from NOAA and Air Force Reserve Hurricane Hunter aircraft indicated that the maximum sustained winds are near 150 mph (240 km/h) with higher gusts. Ida is an extremely dangerous category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Some slight additional strengthening is still possible before Ida moves onshore along the Louisiana coast. Rapid weakening is expected after landfall. Hurricane-force winds extend outward up to 50 miles (85 km) from the center and tropical-storm-force winds extend outward up to 150 miles (240 km). An elevated NOAA C-MAN station at Southwest Pass recently reported a sustained wind of 105 mph (169 km/h) and a wind gust of 121 mph (194 km/h). A station in Shell Beach, Louisiana, recently reported a sustained wind of 44 mph (70 km/h) and a gust of 52 mph (83 km/h). A NOAA National Ocean Service tide gauge in Shell Beach, Louisiana, recently reported a water level of 5.6 feet above mean higher high water, which is an approximation of inundation in that area. The latest minimum central pressure reported by an Air Force Reserve reconnaissance aircraft is 933 mb (27.55 inches). HAZARDS AFFECTING LAND ---------------------- Key messages for Ida can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT4, WMO header WTNT44 KNHC, and on the web at hurricanes.gov/graphics_at4.shtml?key_messages. 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... Port Fourchon, LA to Mouth of the Mississippi River...12-16 ft Morgan City, LA to Port Fourchon, LA...8-12 ft Mouth of the Mississippi River to Bay St. Louis, MS including Lake Borgne...8-12 ft Bay St. Louis, MS to Ocean Springs, MS...6-9 ft Burns Point, LA to Morgan City, LA...5-8 ft Lake Pontchartrain...5-8 ft Ocean Springs, MS to MS/AL border...4-7 ft Lake Maurepas...4-6 ft East of Intracoastal City, LA to Burns Point, LA including Vermilion Bay...3-5 ft MS/AL border to AL/FL border including Mobile Bay...3-5 ft Rockefeller Wildlife Refuge, LA to Intracoastal City, LA...1-3 ft AL/FL border to Okaloosa/Walton County Line including Pensacola Bay...1-3 ft Overtopping of local levees outside of the Hurricane and Storm Damage Risk Reduction System is possible where local inundation values may be higher than those shown above. 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: Catastrophic wind damage is likely where the core of Ida moves onshore along the southeast coast of Louisiana in the next few hours. Hurricane conditions will spread inland within the Hurricane Warning area over southeastern Louisiana through tonight. Tropical storm conditions will also spread inland over portions of Louisiana and Mississippi tonight and Monday. RAINFALL: Heavy rainfall from Ida will continue to impact the southeast Louisiana coast this morning, spreading northeast into the Lower Mississippi Valley later today into Monday. Total rainfall accumulations of 10 to 18 inches with isolated maximum amounts of 24 inches are possible across southeast Louisiana into far southern Mississippi through Monday. This is likely to result in life-threatening flash and urban flooding and significant riverine flooding impacts. Ida is forecast to turn to the northeast early Monday and track across the Middle Tennessee Valley and Upper Ohio Valley through Wednesday, producing the following rainfall totals: Coastal Alabama to the far western Florida panhandle: 5 to 10 inches with isolated maximum amounts of 15 inches, today through Tuesday morning. Central Mississippi: 4 to 8 inches with isolated maximum amounts of 12 inches, tonight through Monday night. Middle Tennessee Valley, Upper Ohio Valley, Central Appalachians into the Mid-Atlantic: 3 to 6 inches with isolated higher amounts, Tuesday into Wednesday. These rainfall totals will result in considerable flash and riverine flooding. TORNADOES: Tornadoes will be most likely through Monday over southeast Louisiana, southern Mississippi, southwest Alabama, and the western Florida Panhandle. A few tornadoes are also possible farther north across much of Mississippi and Alabama on Monday. SURF: Swells will affect the northern Gulf coast through early Monday. 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 100 PM CDT. Next complete advisory at 400 PM CDT. $$ Forecaster Brown

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