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Tropical Storm Sally Forecast Discussion Number 6

2020-09-13 04:38:29| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sat Sep 12 2020 000 WTNT44 KNHC 130238 TCDAT4 Tropical Storm Sally Discussion Number 6 NWS National Hurricane Center Miami FL AL192020 1100 PM EDT Sat Sep 12 2020 Sally's structure remains somewhat disorganized this evening. While there has been a recent increase in deep convection near the low- level center, there is a large CDO feature with -70 to -80C tops displaced 50 to 60 miles to the south and southeast. This structure could be due to the 10 to 15 kt of northwesterly shear analyzed by the SHIPS model and UW-CIMSS. The initial intensity remains 35 kt based on the latest Dvorak estimates from TAFB and SAB, and the central pressure of 1003 mb is based on surface observations in the Naples area as the center passed offshore before 00Z. An Air Force Reserve Hurricane Hunter aircraft will be investigating Sally overnight to provide more information on the storm's intensity and structure. Given the current structure, only gradual strengthening is expected in the short term. However, once the cyclone develops more of an inner core, it should be able to take advantage of warm SSTs and low shear over the Gulf of Mexico during the next couple of days. Steady intensification to hurricane strength is forecast through 48 hours, with a leveling off of the intensity in 60-72 hours as the shear is expected to increase. Overall, the intensity guidance is a little less bullish this cycle, with the HWRF more aggressive while the remainder of the guidance shows a slower rate of intensification. The NHC intensity forecast through landfall remains unchanged from the previous advisory, but now lies a little above HCCA and the intensity consensus. The initial motion estimate is a somewhat uncertain 285/07. Sally is currently being steered by a mid-level ridge centered over the Carolinas that will shift eastward and weaken as a longwave trough moves into the eastern United States over the next 24 to 36 hours. During this time, Sally should move generally west-northwestward or northwestward with a decrease in forward speed on Monday. By 48 hours, the trough lifts out and a narrow ridge builds in north and east of Sally, which should result in the tropical cyclone turning north-northwestward and then northward at less than 5 kt as it approaches the north-central Gulf Coast and moves inland over the Mississippi Valley. After that time, the next trough should induce a faster northeastward motion by day 5. There is a fair bit of spread in the track guidance after 24 hours, with the COAMPS-TC well to the right and the GEFS ensemble mean and UKMET to the left. However, the GFS and ECMWF are in good agreement through 60 hours near the middle of the guidance envelope. The NHC track is similar to the previous one and lies in the middle of the guidance and is near the TVCA multi-model consensus and HCCA. Users are reminded to not focus on the exact details of the track or intensity forecasts, as the average NHC track error at 72 h is around 110 miles and the average intensity error is around 15 mph. In addition, wind, storm surge, and rainfall hazards will extend far from the center. Unfortunately, confidence is increasing that Sally's expected slow forward speed near the Gulf Coast will exacerbate the storm surge and heavy rainfall threats. KEY MESSAGES: 1. Life-threatening storm surge is possible along the Gulf Coast beginning on Monday, and a Storm Surge Watch is in effect for areas outside the southeastern Louisiana Hurricane and Storm Damage Risk Reduction System from the Mouth of the Mississippi River to the Alabama/Florida border. Residents in these areas should follow any advice given by local officials. 2. Hurricane conditions are possible by early Tuesday from Grand Isle, Louisiana to the Alabama/Florida border, including Metropolitan New Orleans, with tropical storm conditions possible by Monday. 3. Sally is expected to produce flash flooding across portions of southern Florida and prolong existing minor river flooding across central Florida through Sunday. Flash and urban flooding and minor to moderate river flooding are likely across portions of the central Gulf Coast from Sunday through the middle of next week. 4. Tropical storm conditions are possible early next week in portions of the Florida Panhandle, where a Tropical Storm Watch is in effect. Wind gusts to tropical storm force could occur over portions of the lower Florida Keys overnight. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 26.3N 82.9W 35 KT 40 MPH 12H 13/1200Z 27.0N 84.4W 40 KT 45 MPH 24H 14/0000Z 27.7N 86.0W 50 KT 60 MPH 36H 14/1200Z 28.3N 87.5W 60 KT 70 MPH 48H 15/0000Z 28.8N 88.6W 70 KT 80 MPH 60H 15/1200Z 29.4N 89.2W 75 KT 85 MPH 72H 16/0000Z 30.1N 89.5W 75 KT 85 MPH 96H 17/0000Z 31.7N 89.1W 50 KT 60 MPH...INLAND 120H 18/0000Z 33.5N 86.5W 25 KT 30 MPH...INLAND $$ Forecaster Brennan

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Tropical Depression Sixteen-E Forecast Discussion Number 1

2020-09-13 04:38:29| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Sat Sep 12 2020 000 WTPZ41 KNHC 130238 TCDEP1 Tropical Depression Sixteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP162020 900 PM MDT Sat Sep 12 2020 The last few visible satellite images indicated convection growing closer to the center of a low pressure area that NHC has been tracking for the past few days. Since the low was already well-defined this afternoon, the development of organized deep convection means that a tropical depression has formed. The initial wind speed is set to 30 kt, which is a blend of the TAFB/SAB fixes and earlier ASCAT data. The depression is embedded within a moderate easterly wind-shear environment, partially related to its position in the larger ITCZ/monsoon trough structure. Global model guidance is in reasonable agreement on the large-scale circulation becoming focused on the new tropical cyclone and a slight relaxation of the shear during the next couple of days. This change should lead to gradual intensification, and the new forecast is between the model consensus and the corrected-consensus aids. Beyond 2-3 days, decreasing SSTs and increasing dry air entrainment should promote weakening, and that is reflected below. The initial motion estimate is an uncertain northwestward or 315/08 kt. A mid-level ridge is forecast to build westward, causing the cyclone to move west-northwestward for a few days after the weekend. A westward turn is forecast at long range due to the shallow cyclone feeling the low-level ridge. One big uncertainty with this forecast is how it interacts with the larger ITCZ/monsoon trough circulation, including the remnants of Invest 91E. For now, it is assumed that only a slight slow down occurs as the depression becomes the dominant circulation in the area, and the forecast is more consistent with the GFS- or UKMET-based guidance. However, a slower ECMWF-like solution is also possible, but is being given less weight at this time. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 16.7N 112.9W 30 KT 35 MPH 12H 13/1200Z 17.5N 113.8W 35 KT 40 MPH 24H 14/0000Z 18.3N 115.4W 40 KT 45 MPH 36H 14/1200Z 18.9N 116.9W 45 KT 50 MPH 48H 15/0000Z 19.5N 118.5W 50 KT 60 MPH 60H 15/1200Z 20.0N 119.9W 55 KT 65 MPH 72H 16/0000Z 20.5N 121.0W 55 KT 65 MPH 96H 17/0000Z 21.5N 123.5W 45 KT 50 MPH 120H 18/0000Z 21.5N 126.0W 30 KT 35 MPH $$ Forecaster Blake

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Tropical Depression Sixteen-E Forecast Advisory Number 1

2020-09-13 04:37:02| National Hurricane Center (East Pacific)

Issued at 0300 UTC SUN SEP 13 2020 000 WTPZ21 KNHC 130236 TCMEP1 TROPICAL DEPRESSION SIXTEEN-E FORECAST/ADVISORY NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162020 0300 UTC SUN SEP 13 2020 THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT. TROPICAL DEPRESSION CENTER LOCATED NEAR 16.7N 112.9W AT 13/0300Z POSITION ACCURATE WITHIN 30 NM PRESENT MOVEMENT TOWARD THE NORTHWEST OR 315 DEGREES AT 8 KT ESTIMATED MINIMUM CENTRAL PRESSURE 1004 MB MAX SUSTAINED WINDS 30 KT WITH GUSTS TO 40 KT. 12 FT SEAS.. 0NE 80SE 0SW 0NW. WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT. REPEAT...CENTER LOCATED NEAR 16.7N 112.9W AT 13/0300Z AT 13/0000Z CENTER WAS LOCATED NEAR 16.4N 112.6W FORECAST VALID 13/1200Z 17.5N 113.8W MAX WIND 35 KT...GUSTS 45 KT. 34 KT... 20NE 60SE 60SW 20NW. FORECAST VALID 14/0000Z 18.3N 115.4W MAX WIND 40 KT...GUSTS 50 KT. 34 KT... 70NE 90SE 90SW 40NW. FORECAST VALID 14/1200Z 18.9N 116.9W MAX WIND 45 KT...GUSTS 55 KT. 34 KT... 80NE 90SE 90SW 60NW. FORECAST VALID 15/0000Z 19.5N 118.5W MAX WIND 50 KT...GUSTS 60 KT. 50 KT... 30NE 30SE 20SW 20NW. 34 KT... 80NE 80SE 80SW 80NW. FORECAST VALID 15/1200Z 20.0N 119.9W MAX WIND 55 KT...GUSTS 65 KT. 50 KT... 40NE 30SE 20SW 30NW. 34 KT... 90NE 70SE 60SW 80NW. FORECAST VALID 16/0000Z 20.5N 121.0W MAX WIND 55 KT...GUSTS 65 KT. 50 KT... 40NE 30SE 20SW 30NW. 34 KT... 90NE 70SE 60SW 80NW. EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 100 NM ON DAY 4 AND 150 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY OUTLOOK VALID 17/0000Z 21.5N 123.5W MAX WIND 45 KT...GUSTS 55 KT. OUTLOOK VALID 18/0000Z 21.5N 126.0W MAX WIND 30 KT...GUSTS 40 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 16.7N 112.9W NEXT ADVISORY AT 13/0900Z $$ FORECASTER BLAKE

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Tropical Depression Rene Forecast Discussion Number 24

2020-09-13 04:35:00| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sat Sep 12 2020 000 WTNT43 KNHC 130234 TCDAT3 Tropical Depression Rene Discussion Number 24 NWS National Hurricane Center Miami FL AL182020 1100 PM AST Sat Sep 12 2020 Satellite images indicate that a band of convection has recently increased on the western side of the circulation, otherwise the center remains mostly exposed. The initial wind speed is reduced to 25 kt based on scatterometer data. The small cyclone is likely to gradually spin down due to persistent moderate shear and a fairly dry environment. The hostile conditions are not likely to change too much, so Rene is forecast to lose all convection in a day or two and become a remnant low. The new NHC intensity forecast is lower than the previous one due to the weaker initial intensity and follows the latest global model consensus. The depression is moving northwestward at about 11 kt. A blocking ridge of high pressure is forecast to build to the northwest or Rene, causing the cyclone to slow down and then turn westward and west-southwestward early next week. The guidance is similar to the previous package, and no significant track changes were made to the official NHC forecast. The forecast still might hold onto the circulation too long, and the remnant low could dissipate into a trough of low pressure sooner than indicated below. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 25.3N 46.4W 25 KT 30 MPH 12H 13/1200Z 26.4N 47.3W 25 KT 30 MPH 24H 14/0000Z 27.3N 48.1W 25 KT 30 MPH 36H 14/1200Z 27.4N 48.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 15/0000Z 27.2N 49.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 15/1200Z 26.5N 50.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 16/0000Z...DISSIPATED $$ Forecaster Blake

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Tropical Storm Sally Forecast Advisory Number 6

2020-09-13 04:33:30| National Hurricane Center (Atlantic)

Issued at 0300 UTC SUN SEP 13 2020 520 WTNT24 KNHC 130233 TCMAT4 TROPICAL STORM SALLY FORECAST/ADVISORY NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL192020 0300 UTC SUN SEP 13 2020 CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY... NONE. SUMMARY OF WATCHES AND WARNINGS IN EFFECT... A STORM SURGE WATCH IS IN EFFECT FOR... * MOUTH OF THE MISSISSIPPI RIVER TO THE ALABAMA/FLORIDA BORDER * LAKE PONTCHARTRAIN...LAKE MAUREPAS...AND LAKE BORGNE * MOBILE BAY A HURRICANE WATCH IS IN EFFECT FOR... * GRAND ISLE LOUISIANA TO THE ALABAMA/FLORIDA BORDER * LAKE PONTCHARTRAIN AND LAKE MAUREPAS INCLUDING METROPOLITAN NEW ORLEANS A TROPICAL STORM WATCH IS IN EFFECT FOR... * ALABAMA/FLORIDA BORDER TO OCHLOCKONEE RIVER FLORIDA 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 WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA WITHIN THE NEXT 48 HOURS. TROPICAL STORM CENTER LOCATED NEAR 26.3N 82.9W AT 13/0300Z POSITION ACCURATE WITHIN 35 NM PRESENT MOVEMENT TOWARD THE WEST-NORTHWEST OR 285 DEGREES AT 7 KT ESTIMATED MINIMUM CENTRAL PRESSURE 1003 MB MAX SUSTAINED WINDS 35 KT WITH GUSTS TO 45 KT. 34 KT....... 0NE 70SE 0SW 0NW. WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT. REPEAT...CENTER LOCATED NEAR 26.3N 82.9W AT 13/0300Z AT 13/0000Z CENTER WAS LOCATED NEAR 26.0N 82.4W FORECAST VALID 13/1200Z 27.0N 84.4W MAX WIND 40 KT...GUSTS 50 KT. 34 KT... 40NE 70SE 0SW 30NW. FORECAST VALID 14/0000Z 27.7N 86.0W MAX WIND 50 KT...GUSTS 60 KT. 50 KT... 20NE 0SE 0SW 0NW. 34 KT... 80NE 90SE 20SW 80NW. FORECAST VALID 14/1200Z 28.3N 87.5W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 40NE 20SE 10SW 30NW. 34 KT... 90NE 80SE 30SW 70NW. FORECAST VALID 15/0000Z 28.8N 88.6W MAX WIND 70 KT...GUSTS 85 KT. 64 KT... 20NE 10SE 10SW 20NW. 50 KT... 40NE 30SE 20SW 30NW. 34 KT... 80NE 80SE 40SW 60NW. FORECAST VALID 15/1200Z 29.4N 89.2W MAX WIND 75 KT...GUSTS 90 KT. 50 KT... 40NE 30SE 10SW 30NW. 34 KT... 80NE 90SE 30SW 50NW. FORECAST VALID 16/0000Z 30.1N 89.5W MAX WIND 75 KT...GUSTS 90 KT. 50 KT... 40NE 40SE 20SW 30NW. 34 KT... 70NE 90SE 40SW 50NW. EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 150 NM ON DAY 4 AND 175 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY OUTLOOK VALID 17/0000Z 31.7N 89.1W...INLAND MAX WIND 50 KT...GUSTS 60 KT. OUTLOOK VALID 18/0000Z 33.5N 86.5W...INLAND MAX WIND 25 KT...GUSTS 35 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 26.3N 82.9W INTERMEDIATE PUBLIC ADVISORY...WTNT34 KNHC/MIATCPAT4...AT 13/0600Z NEXT ADVISORY AT 13/0900Z $$ FORECASTER BRENNAN

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