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Hurricane Delta Forecast Discussion Number 14

2020-10-08 04:49:29| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Wed Oct 07 2020 000 WTNT41 KNHC 080249 TCDAT1 Hurricane Delta Discussion Number 14 NWS National Hurricane Center Miami FL AL262020 1000 PM CDT Wed Oct 07 2020 Observations from an Air Force Reserve Unit Hurricane Hunter aircraft indicate that Delta is gradually strengthening while it moves over the open waters of the south-central Gulf of Mexico. Based on a blend of adjusted flight-level and SFMR wind measurements from the plane, the current intensity is set at 80 kt. The cloud pattern of the hurricane continues to become better organized on satellite images, with a growing Central Dense Overcast, and convective banding features becoming better defined, particularly over the northern semicircle of the circulation. Additional intensification is likely while Delta moves through a favorable environment during the next day or so, and the official forecast is fairly close to the corrected consensus guidance, HCCA. 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. The NHC intensity forecast is above the numerical guidance in 36-48 hours. It should be noted that 1-2 day tropical cyclone intensity forecasts are subject to errors of around 1 Saffir-Simpson category. The global models show a further increase in the size of the hurricane while it moves into the northern Gulf. The official wind radii forecasts are based on a consensus of these model predictions. The latest center fixes from the Hurricane Hunters show a west-northwestward motion, at about 300/15 kt. Delta should turn toward the north-northwest and north over the next 36 hours or so while moving around the western periphery of a subtropical high pressure system centered over Florida. When the hurricane moves into the northern Gulf of Mexico on Friday, Delta should turn toward the north-northeast on the southeastern side of a mid-tropospheric shortwave over the southern United States. The official track forecast is close to both the simple and corrected dynamical model consensus predictions, TVCA and HCCA, respectively. These objective aids are in close agreement with one another. Based on the official forecast, it is time to issue storm surge and hurricane warnings for a portion of the northern Gulf of Mexico coast. 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. 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 to Middle Mississippi Valley. As Delta moves farther inland, additional heavy rainfall is expected in the Ohio Valley and Mid Atlantic this weekend. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 22.5N 90.9W 80 KT 90 MPH 12H 08/1200Z 23.7N 92.2W 95 KT 110 MPH 24H 09/0000Z 25.4N 93.4W 105 KT 120 MPH 36H 09/1200Z 27.5N 93.5W 100 KT 115 MPH 48H 10/0000Z 30.0N 92.7W 85 KT 100 MPH 60H 10/1200Z 32.4N 91.5W 35 KT 40 MPH...INLAND 72H 11/0000Z 34.2N 89.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 12/0000Z 37.5N 85.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 13/0000Z...DISSIPATED $$ Forecaster Pasch

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Tropical Depression Norbert Forecast Discussion Number 10

2020-10-08 04:40:34| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Wed Oct 07 2020 000 WTPZ44 KNHC 080240 TCDEP4 Tropical Depression Norbert Discussion Number 10 NWS National Hurricane Center Miami FL EP192020 900 PM MDT Wed Oct 07 2020 Tropical Depression Norbert is still struggling to maintain any deep convection near its center. Satellite imagery indicates the low-level center remains exposed, and a small convective burst noted in recent infrared imagery is already collapsing. The initial intensity is perhaps generously held at 30 kt based on a blend of recent objective satellite estimates and Dvorak classifications from TAFB and SAB. Overnight scatterometer data should help further assess whether additional weakening has occurred. Norbert continues to meander within a weak steering pattern, and its center has drifted southeast of the previous advisory position. Little movement is expected during the next 12 h, but Norbert should begin slowly moving west-southwestward from 12-36 h. Then, the cyclone should move west-northwestward or northwestward at around 5 kt for the remainder of the forecast period as a mid-level ridge builds to the north and northeast of Norbert. No significant changes were made to the NHC track forecast with this advisory. Although current satellite trends do not bode well for Norbert, the system remains embedded in a favorable environment of warm water and light vertical wind shear. The latest SHIPS guidance suggests the deep-layer shear will increase slightly during the next 24 h, which combined with any more dry air intrusions could cause Norbert to degenerate into a remnant low. On the other hand, increasing mid-level moisture and weaker shear beyond this time period could allow for a convective burst capable of getting Norbert back to minimal tropical storm strength. Given the mixed signals for small intensity fluctuations in either direction, the official intensity forecast holds Norbert's intensity steady for the next several days. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 13.2N 106.8W 30 KT 35 MPH 12H 08/1200Z 13.2N 106.8W 30 KT 35 MPH 24H 09/0000Z 13.1N 107.1W 30 KT 35 MPH 36H 09/1200Z 13.0N 107.6W 30 KT 35 MPH 48H 10/0000Z 13.2N 108.4W 30 KT 35 MPH 60H 10/1200Z 13.9N 109.1W 30 KT 35 MPH 72H 11/0000Z 14.9N 109.7W 30 KT 35 MPH 96H 12/0000Z 16.5N 110.5W 30 KT 35 MPH 120H 13/0000Z 17.0N 111.5W 25 KT 30 MPH $$ Forecaster Reinhart/Berg

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Tropical Depression Norbert Forecast Discussion Number 9

2020-10-07 22:50:51| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Wed Oct 07 2020 000 WTPZ44 KNHC 072050 TCDEP4 Tropical Depression Norbert Discussion Number 9 NWS National Hurricane Center Miami FL EP192020 300 PM MDT Wed Oct 07 2020 Convection has decreased in association with Norbert since the last advisory, with the system now comprised of a mostly-exposed swirl of low-level clouds. Based on the weakened cloud pattern, the initial intensity is reduced to 30 kt and Norbert is downgraded to a depression. Daytime visible imagery shows that Norbert is south of the previous advisory location, and the initial motion is a somewhat uncertain 180/2. Little motion is expected during the next 12 h or so as the cyclone is in an area of weak steering currents. A west-southwestward drift is forecast from 12-36 h. This will be followed by a slow motion toward the west-northwest or northwest for the remainder of the forecast period as a mid-level ridge builds to the north and northeast of Norbert. The forecast guidance has shifted to the right at 96 and 120 h, so the new forecast track is shifted in that direction as well. Otherwise, the new forecast, which lies near the various consensus models, has only slight changes since the previous advisory. While Norbert is seemingly in a favorable environment of light vertical wind shear over warm water, none of the intensity guidance calls for significant strengthening. Indeed, the GFS and ECMWF models call for the system to dissipate before 120 h, possibly due to dry air intrusions. Given the favorable shear and sea surface temperatures, the official intensity forecast calls for the system to survive for 5 days with little change in strength in overall agreement with the intensity guidance. It should be noted that if any strong convective bursts occur, these could cause the system to strengthen just the little bit it needs to regain tropical storm strength. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 13.4N 107.1W 30 KT 35 MPH 12H 08/0600Z 13.4N 107.1W 30 KT 35 MPH 24H 08/1800Z 13.3N 107.4W 30 KT 35 MPH 36H 09/0600Z 13.1N 107.8W 30 KT 35 MPH 48H 09/1800Z 13.1N 108.2W 30 KT 35 MPH 60H 10/0600Z 13.8N 108.8W 30 KT 35 MPH 72H 10/1800Z 14.7N 109.6W 30 KT 35 MPH 96H 11/1800Z 16.5N 111.0W 30 KT 35 MPH 120H 12/1800Z 18.0N 112.5W 30 KT 35 MPH $$ Forecaster Beven

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Hurricane Delta Forecast Discussion Number 13

2020-10-07 22:48:20| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Wed Oct 07 2020 000 WTNT41 KNHC 072048 TCDAT1 Hurricane Delta Discussion Number 13 NWS National Hurricane Center Miami FL AL262020 400 PM CDT Wed Oct 07 2020 The center of Delta has moved off the northern coast of the Yucatan peninsula and is now located over the southern Gulf of Mexico. The hurricane remains well organized in satellite imagery with a large curved band wrapping around the center and a fairly symmetric CDO. An Air Force Reserve reconnaissance aircraft has provided a few center fixes this afternoon, and found that Delta's passage over land has resulted in weakening, and the initial wind speed is set at 75 kt, which is based on a peak flight-level wind of 81 kt. The aircraft also reported a minimum pressure of 977 mb on its final center penetration, and data from the plane indicate that there has been some increase in the radius of maximum winds. Re-strengthening is anticipated over the next 24-36 hours while Delta moves within a favorable upper-level environment and over the relatively deep warm waters of the southern and central Gulf of Mexico. Most of the intensity guidance brings Delta back up to major hurricane status, and so does the official forecast. The global models also significantly deepen Delta during the next 36 hours, lending confidence to re-intensification. After 36 hours, increasing shear and cooler waters over the northern Gulf of Mexico are likely to cause some decrease in intensity before Delta makes landfall, however the hurricane's wind field is forecast to expand, which will increase the storm surge and wind threats. Regardless of Delta's landfall intensity, life-threatening storm surge and strong winds are likely over a large portion of the northwestern and northern Gulf coast. Delta has been moving on a consistent northwestward heading of 305 degrees at about 15 kt. Delta should continue on this general heading with some reduction in forward speed tonight and early Thursday as it approaches the western extent of the subtropical ridge. A mid- to upper-level trough over Texas is forecast to slide eastward over the next couple of days, which is expected to cause Delta to turn north-northwestward on Thursday, and northward toward the northern Gulf coast by Friday. A faster northward to north-northeastward motion in 48-60 hours will bring the center onshore along the northern Gulf coast late Friday. The cross track spread in the dynamical models has decreased this cycle, with the model predictions converging on the previous NHC track forecast. Therefore, little change has been made to the previous official forecast, and it lies near the center of the now tightly clustered guidance envelope. Key Messages: 1. Winds and water levels along the northern coast of the Yucatan Peninsula will gradually subside this evening. Heavy rainfall, which could lead to significant flash flooding, will affect the northern Yucatan Peninsula through early Thursday. 2. 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 Watches are in effect, and residents in these areas should follow advice given by local officials. 3. 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 to Middle Mississippi Valley. As Delta moves farther inland, additional heavy rainfall is expected in the Ohio Valley and Mid Atlantic this weekend. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 22.1N 89.5W 75 KT 85 MPH 12H 08/0600Z 23.2N 91.2W 85 KT 100 MPH 24H 08/1800Z 24.8N 92.9W 95 KT 110 MPH 36H 09/0600Z 26.7N 93.4W 100 KT 115 MPH 48H 09/1800Z 29.1N 92.9W 90 KT 105 MPH 60H 10/0600Z 31.6N 91.9W 45 KT 50 MPH...INLAND 72H 10/1800Z 33.7N 90.5W 30 KT 35 MPH...INLAND 96H 11/1800Z 37.0N 85.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 12/1800Z...DISSIPATED $$ Forecaster Brown

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Hurricane Delta Forecast Discussion Number 12

2020-10-07 16:55:10| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Wed Oct 07 2020 721 WTNT41 KNHC 071455 TCDAT1 Hurricane Delta Discussion Number 12 NWS National Hurricane Center Miami FL AL262020 1000 AM CDT Wed Oct 07 2020 Satellite and surface observations show that Delta made landfall along the northeastern coast of the Yucatan peninsula around 1030 UTC near Puerto Morelos. A WeatherFlow observing site at Puerto Morelos reported near calm winds and a minimum pressure of around 972 mb when the center passed that location. Another WeatherFlow site near Cancun reported peak sustained winds of 73 kt with a gust to 92 kt. Hurricane-force winds gusts were also reported at an observing site on Cozumel. Since landfall, Delta has moved across the northeastern portion of the Yucatan peninsula and is now about the emerge off the northern coast of the peninsula into the southern Gulf of Mexico. Assuming some weakening has occurred, the initial intensity has been set at 90 kt, but this could be a little generous. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate Delta early this afternoon. A NOAA P-3 aircraft has been preforming a Tail Doppler Radar mission this morning. Once Delta moves over the southern Gulf of Mexico, warm waters and expected low vertical wind shear conditions are expected to allow for re-strengthening during the next 24 to 36 hours. After 48 hours, increasing southwesterly shear and cooler waters over the northern Gulf are likely to induce some weakening. The intensity guidance has trended downward this cycle, and the NHC forecast has been adjusted accordingly. Delta, however is still expected to regain major hurricane status and the wind field is likely to grow in size during its approach to the northern Gulf coast, which will increase the storm surge and wind threats. Regardless of Delta's landfall intensity, life-threatening storm surge and strong winds are likely over a large portion of the northwestern and northern Gulf coast, which has necessitated the issuance of Storm Surge, Hurricane, and Tropical Storm watches for portions of that area. Delta is moving northwestward or 305/15 kt. The hurricane should continue moving northwestward around the southwestern portion of a subtropical ridge that extends over Florida and the northeastern Gulf of Mexico through early Thursday. After that time, a developing mid-level trough over the south-central United States should cause Delta to slow down and turn north-northwestward on Thursday. Delta is forecast to begin accelerating northward or north-northeastward toward the northern Gulf coast ahead of the trough Thursday night and Friday. There has been little change to the early portion of the track forecast, but there has been a little westward shift in the guidance envelope after 24 hours, and the NHC forecast has been moved in that direction. The new forecast track lies near or just left of the TVCA multi-model consensus and a little right of the HFIP corrected consensus aid, again close to the GFS, GFS ensemble mean, and UKMet models. Key Messages: 1. Life-threatening storm surge and dangerous winds will continue within portions of the northern Yucatan Peninsula of Mexico into early afternoon. Heavy rainfall, which could lead to significant flash flooding, will affect the northern Yucatan Peninsula through early Thursday. 2. Delta is expected to grow in size as it approaches the northern Gulf Coast, where there is an increasing likelihood of life- threatening storm surge and dangerous hurricane-force winds beginning Friday, particularly for portions of the Louisiana coast. Storm Surge and Hurricane Watches are in effect, and residents in these areas should follow advice given by local officials. 3. Flash, urban, small stream, and minor river flooding is likely Friday through Saturday from portions of the central Gulf Coast northward into portions of the Lower to Middle Mississippi Valley. As Delta moves farther inland, additional heavy rainfall is expected in the Ohio Valley and Mid Atlantic this weekend. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 21.4N 88.0W 90 KT 105 MPH...INLAND 12H 08/0000Z 22.8N 90.2W 95 KT 110 MPH...OVER WATER 24H 08/1200Z 24.3N 92.4W 100 KT 115 MPH 36H 09/0000Z 26.0N 93.3W 105 KT 120 MPH 48H 09/1200Z 28.1N 93.3W 105 KT 120 MPH 60H 10/0000Z 30.8N 92.4W 70 KT 80 MPH...INLAND 72H 10/1200Z 33.2N 90.9W 40 KT 45 MPH...INLAND 96H 11/1200Z 36.5N 86.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 12/1200Z 39.5N 81.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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