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Tropical Storm Norbert Forecast Discussion Number 8

2020-10-07 16:47:39| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Wed Oct 07 2020 323 WTPZ44 KNHC 071447 TCDEP4 Tropical Storm Norbert Discussion Number 8 NWS National Hurricane Center Miami FL EP192020 900 AM MDT Wed Oct 07 2020 Norbert has recovered somewhat from the dry air intrusion that occurred last night. A new burst of deep convection developed near the center early this morning, but the associated cloud tops are beginning to warm and the convection is becoming displaced over the northeastern portion of the circulation. The initial intensity is being held at 35 kt, and is based off the Dvorak intensity estimates from TAFB, SAB, and the UW-CIMSS ADT. The storm is struggling to stay organized despite being over warm waters and in an environment of relatively low shear. By Thursday, the SHIPS guidance suggests that the shear will increase to around 10-15 kt. This shear, along with occasional dry air intrusions similar to one experienced last night, could gradually weaken the system. On the other hand, the warm waters could counteract the moderately negative environmental factors. The latest NHC forecast still favors the latter scenario, and shows Norbert remaining a 35-kt tropical storm throughout the forecast period. This intensity forecast is unchanged from the previous one, and is a compromise between the SHIPS guidance and the model consensus. The initial motion is stationary, although the exact center location has been difficult to pinpoint this morning. The steering flow is forecast to remain very weak over the next couple of days, and most of the models show little movement through tonight followed by a slow westward drift Wednesday through Thursday. By late this week, a mid-level ridge is forecast to build to the north to northeast of the cyclone, which should force Norbert on a west-northwestward track. The latest NHC track forecast is near the previous one through 72 h, but was adjusted a little north after that time due to a northward shift in the guidance. However, the new track forecast remains south of the consensus aids late in the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 14.2N 107.1W 35 KT 40 MPH 12H 08/0000Z 14.1N 107.1W 35 KT 40 MPH 24H 08/1200Z 14.0N 107.2W 35 KT 40 MPH 36H 09/0000Z 13.9N 107.5W 35 KT 40 MPH 48H 09/1200Z 13.8N 107.9W 35 KT 40 MPH 60H 10/0000Z 14.1N 108.5W 35 KT 40 MPH 72H 10/1200Z 14.9N 109.3W 35 KT 40 MPH 96H 11/1200Z 16.5N 111.0W 35 KT 40 MPH 120H 12/1200Z 17.5N 112.2W 35 KT 40 MPH $$ Forecaster Latto

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Hurricane Delta Forecast Discussion Number 11

2020-10-07 10:59:38| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Wed Oct 07 2020 000 WTNT41 KNHC 070859 TCDAT1 Hurricane Delta Discussion Number 11 NWS National Hurricane Center Miami FL AL262020 400 AM CDT Wed Oct 07 2020 Satellite images show very deep convection associated with Delta, with extremely cold cloud-top temperatures to -97C noted southwest of the center overnight. However, this structure has not resulted in a stronger cyclone, and the full NOAA Hurricane Hunter aircraft mission actually indicated that Delta has significantly weakened since earlier today. The maximum flight-level winds were 98 kt, with SFMR values near 90 kt. Early in the mission, the flight director indicated that the eyewall had dissipated, but on the last fix, she noted that the eyewall had re-formed. Recent Cuban radar data also indicate that at least a partial eyewall is present, so the initial wind speed is generously kept at 100 kt. Delta should begin to re-intensify late today as it moves into an area of fairly warm and deep waters, with fairly light shear. The regional hurricane models all show Delta attaining category 4 status in 36-48 hours, and so does the NHC forecast. As Delta approaches the Louisiana coast, lower oceanic heat content and an increase in shear is likely to cause some weakening before landfall. The NHC intensity forecast is very similar to the previous one, and leans on the stronger regional hurricane models. I should also note that all of the guidance show Delta becoming considerably larger than it is now by the time it reaches the northern Gulf coast, so even if weakening occurs there, the hurricane will likely bring a sizable area of hazardous conditions to the coast. Fixes from the aircraft and Cuban radar data indicate the storm is moving faster to the northwest or 305/15 kt. Delta should make landfall during the next few hours between Cozumel and Cancun, and move quickly across northeastern Yucatan before emerging in the southern Gulf of Mexico early this afternoon. The hurricane is then expected to move to the northwest or west-northwest around the southwestern and western portion of the subtropical ridge for about the next 36 hours. Thereafter, Delta will likely turn northward by early Friday between the ridge and a mid-level trough over Texas. While there is broad agreement on the synoptic pattern, subtle differences in the subtropical ridge and the depth of the cyclone are causing some challenges. The ECMWF and its ensembles, for instance, are showing a stronger ridge and a weaker storm, which results in a slower track toward southwestern Louisiana. The GFS and UKMET, on the other hand, are showing a deeper cyclone, which would feel stronger upper-level winds, and move Delta faster to the coast. Given the expectation of a powerful cyclone at landfall, the NHC forecast is shaded toward the latter two models, which results in a slightly faster and westward-shifted forecast from before, not too different from the model consensus. Key Messages: 1. Life-threatening storm surge and dangerous winds are expected within portions of the northern Yucatan Peninsula of Mexico during the next few hours. Now is the time to be in your storm shelter. 2. Heavy rainfall will affect portions of western Cuba and the northern Yucatan Peninsula through early Thursday. This rainfall could lead to significant flash flooding and mudslides. Flash, urban, and small stream flooding, along with minor river flooding is likely Friday through Saturday across portions of the central Gulf Coast north into portions of the Lower Mississippi Valley. The heavy rainfall will spread northeastward into the Tennessee Valley and interior southeastern United States this weekend into early next week. 3. There is an increasing likelihood of life-threatening storm surge and dangerous hurricane-force winds, especially along the coasts of Louisiana and Mississippi, beginning on Friday. Residents in these areas should ensure they have their hurricane plan in place and follow advice given by local officials. Storm surge and hurricane watches will likely be issued for portions of the northern Gulf Coast later today. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 20.6N 86.4W 100 KT 115 MPH 12H 07/1800Z 21.9N 88.4W 90 KT 105 MPH 24H 08/0600Z 23.3N 90.8W 95 KT 110 MPH 36H 08/1800Z 24.9N 92.4W 105 KT 120 MPH 48H 09/0600Z 26.7N 92.9W 115 KT 130 MPH 60H 09/1800Z 29.2N 92.3W 100 KT 115 MPH 72H 10/0600Z 32.0N 91.0W 50 KT 60 MPH...INLAND 96H 11/0600Z 35.5N 87.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 12/0600Z 38.5N 82.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake

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Tropical Storm Norbert Forecast Discussion Number 7

2020-10-07 10:48:12| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Wed Oct 07 2020 000 WTPZ44 KNHC 070848 TCDEP4 Tropical Storm Norbert Discussion Number 7 NWS National Hurricane Center Miami FL EP192020 300 AM MDT Wed Oct 07 2020 Norbert has weakened as entrainment of dry air has disrupted the compact system. The center was partially exposed overnight, but recent infrared imagery shows a new burst of deep convection near the center. Microwave imagery and ASCAT scatterometer wind data indicated the center had drifted southwest from its previous position, as the storm is beginning to meander within the weak steering flow. The initial intensity has been lowered to 35 kt based on the recent ASCAT-A overpass that showed a peak wind of 33 kt, as well as a T2.5 Dvorak estimate from TAFB. The intensity forecast for Norbert remains tricky given its small circulation and the presence of dry air in the surrounding environment. Sea-surface temperatures are more than sufficient for at least modest strengthening, but the question will be whether Norbert can survive the increased southeasterly shear that the SHIPS guidance calls for during the next 24-48 h. If so, Norbert may remain a tropical storm through the next 5 days. Alternatively, the shear and additional bouts of dry air entrainment could weaken the system to a depression or even a remnant low late in the forecast period. While small intensity changes due to diurnal fluctuations in convection are certainly possible, the official NHC forecast keeps Norbert's intensity forecast at 35 kt in consideration of the mixed signals noted in the latest intensity guidance. As previously mentioned, the center of Norbert has drifted to the southwest overnight. The storm is expected to remain nearly stationary over the next couple of days as distant Hurricane Delta over the northwestern Caribbean Sea has weakened the ridge that had been steering Norbert. Therefore, the forecast track through 48 h is more uncertain than usual given the potential for erratic motion as indicated by the diverging model solutions. By Friday, Norbert should begin moving slowly westward or west-northwestward as the ridge gradually builds to the north. The NHC track forecast remains fairly close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 14.0N 107.1W 35 KT 40 MPH 12H 07/1800Z 13.9N 107.2W 35 KT 40 MPH 24H 08/0600Z 13.9N 107.3W 35 KT 40 MPH 36H 08/1800Z 14.0N 107.6W 35 KT 40 MPH 48H 09/0600Z 14.0N 108.0W 35 KT 40 MPH 60H 09/1800Z 14.1N 108.7W 35 KT 40 MPH 72H 10/0600Z 14.6N 109.5W 35 KT 40 MPH 96H 11/0600Z 15.5N 111.0W 35 KT 40 MPH 120H 12/0600Z 16.5N 112.5W 35 KT 40 MPH $$ Forecaster Reinhart/Stewart

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Hurricane Delta Forecast Discussion Number 10

2020-10-07 04:48:05| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Tue Oct 06 2020 000 WTNT41 KNHC 070247 TCDAT1 Hurricane Delta Discussion Number 10 NWS National Hurricane Center Miami FL AL262020 1000 PM CDT Tue Oct 06 2020 Observations from a NOAA Hurricane Hunter aircraft and conventional and microwave satellite imagery indicate that Delta has not intensified since earlier today. The central pressure has risen somewhat and the current intensity estimate, 115 kt, is probably generous based on flight-level and SFMR-observed surface winds from the NOAA plane. Although the hurricane continues to have very deep convection near and over the center, the cloud pattern lacks well-defined banding features, and an eye is not evident on either geostationary or polar-orbiting satellite images. Surveillance data from the NOAA G-IV aircraft suggest that Delta's circulation does not extend as markedly into the upper troposphere as one would expect for a major hurricane. Given the current state of the system, not much strengthening seems likely before the center reaches northeastern Yucatan tomorrow morning. Some weakening is likely due to the interaction with land during the next 12-18 hours. Re-intensification over the southern Gulf of Mexico is still expected, but when Delta reaches the northern Gulf, lower oceanic heat content is likely to cause at least slight weakening. The official intensity forecast is somewhat above most of the model guidance, but not much different from the regional hurricane models, HWRF and HMON, over the northern Gulf. Fixes from the aircraft indicate a continued west-northwestward motion at just a slightly slower forward speed, 300/14 kt. The track forecast reasoning is basically unchanged from earlier today. Delta should move along and around the southwestern and western periphery of a mid-tropospheric anticyclone centered just east of Florida for the next couple of days. Around 72 hours, the flow ahead of a shortwave trough over the south-central United States should cause the tropical cyclone to turn north-northeastward and move across the central Gulf coast late Friday or early Saturday. The official track forecast remains close to the dynamical model consensus, TVCA. Key Messages: 1. Life-threatening storm surge and potentially catastrophic wind damage are expected within portions of the northern Yucatan Peninsula of Mexico beginning tonight. All preparations to protect life and property should be rushed to completion. 2. Heavy rainfall will affect portions of the Cayman Islands, western Cuba and the northern Yucatan Peninsula through midweek. This rainfall could lead to significant flash flooding and mudslides. The potential for heavy rain, flash and possible minor river flooding will increase across portions of the central Gulf Coast, Tennessee Valley, and southeastern United States as Delta moves inland later this week. 3. There is an increasing likelihood of life-threatening storm surge and dangerous hurricane-force winds, especially along the coasts of Louisiana and Mississippi, beginning on Friday. Residents in these areas should ensure they have their hurricane plan in place and follow advice given by local officials. Storm surge and hurricane watches will likely be issued for portions of the northern Gulf Coast on Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 19.5N 85.1W 115 KT 130 MPH 12H 07/1200Z 20.9N 87.1W 115 KT 130 MPH...INLAND 24H 08/0000Z 22.3N 89.8W 105 KT 120 MPH...OVER WATER 36H 08/1200Z 23.6N 91.7W 110 KT 125 MPH 48H 09/0000Z 25.0N 92.7W 115 KT 130 MPH 60H 09/1200Z 26.8N 92.8W 115 KT 130 MPH 72H 10/0000Z 29.0N 92.2W 110 KT 125 MPH 96H 11/0000Z 33.0N 89.8W 50 KT 60 MPH...INLAND 120H 12/0000Z 36.0N 86.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Pasch

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Post-Tropical Cyclone Marie Forecast Discussion Number 32

2020-10-07 04:46:05| National Hurricane Center (East Pacific)

Issued at 500 PM HST Tue Oct 06 2020 000 WTPZ43 KNHC 070245 TCDEP3 Post-Tropical Cyclone Marie Discussion Number 32 NWS National Hurricane Center Miami FL EP182020 500 PM HST Tue Oct 06 2020 Patchy shower activity continues nearly 250 n mi to the northeast of Marie's center--way too far away and way too weak for the system to still be classified as a tropical cyclone. Marie has therefore become a remnant low, with maximum winds set at 30 kt since an ASCAT-C pass around 1800 UTC did not register any winds of tropical storm force. The remnant circulation is expected to gradually spin down during the next few days due to cold waters, dry air, and southwesterly shear of about 40 kt. The global models generally show the remnant low hanging around for the next 3 days and then opening up into a trough by day 4, and that is reflected in this last NHC advisory. Marie continues moving toward the west-northwest, or 300/7 kt. A fairly weak low- to mid-level ridge to the north should keep Marie on a west-northwestward heading for the next 24 hours, followed by a westward motion with a gradual decrease in speed from 36 to 72 hours. Most of the track models seem to pull the remnant low too far to the north during the next day or so, and the NHC track forecast is therefore near the southern side of the guidance envelope, between HCCA and the previous interpolated official forecast. This is the last advisory on Marie. For additional information on the remnant low please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at ocean.weather.gov/shtml/NFDHSFEPI.php FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 22.5N 136.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 12H 07/1200Z 22.9N 137.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 08/0000Z 23.2N 137.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 08/1200Z 23.3N 138.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 09/0000Z 23.3N 139.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 09/1200Z 23.3N 140.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 10/0000Z 23.3N 140.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 11/0000Z...DISSIPATED $$ Forecaster Berg

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