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Tropical Storm Marie Forecast Discussion Number 30

2020-10-06 16:43:50| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Tue Oct 06 2020 000 WTPZ43 KNHC 061443 TCDEP3 Tropical Storm Marie Discussion Number 30 NWS National Hurricane Center Miami FL EP182020 800 AM PDT Tue Oct 06 2020 Marie continues to gradually spin down this morning, and the impressive burst of convection that developed near the surface center last night, now consists of a shrinking cloud mass with significantly warming cloud tops. Assuming some weakening since the last night's METOP-A and B scatterometer passes indicating peak winds of 40 kt, the initial intensity is lowered to 35 kt which is also supported by a blend of the Dvorak intensity estimates from TAFB and SAB. Marie is moving over cool oceanic sea surface temperatures and through a high statically stable air mass. The persistent, harsh vertical shear environment has displaced what remains of the cyclone's associated deep convection well to the northeast of the center. The Statistical-dynamical intensity guidance and the large-scale models are in general agreement with Marie degenerating into a trough of low pressure in 3 days, and the NHC intensity forecast follows suit. The initial motion estimate is estimated to be west-northwestward, or 295/8 kt. There are no significant changes to the previous forecast track or reasoning. The cyclone should continue moving toward the west-northwest through Wednesday evening. Through the remaining portion of the period, the post-tropical remnant low should continue to gradually spin down while moving westward within the low-level easterlies and open up into a trough of low pressure by Friday. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 22.1N 135.1W 40 KT 45 MPH 12H 07/0000Z 22.5N 136.2W 35 KT 40 MPH...POST-TROPICAL 24H 07/1200Z 22.9N 137.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 08/0000Z 23.2N 138.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 08/1200Z 23.2N 138.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 09/0000Z 23.2N 139.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 09/1200Z...DISSIPATED $$ Forecaster Roberts

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Tropical Storm Norbert Forecast Discussion Number 4

2020-10-06 16:43:19| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Tue Oct 06 2020 000 WTPZ44 KNHC 061443 TCDEP4 Tropical Storm Norbert Discussion Number 4 NWS National Hurricane Center Miami FL EP192020 900 AM MDT Tue Oct 06 2020 The overall appearance of Norbert has changed little since early this morning, with a mass of deep convection pulsating over the low-level center. A blend of the latest Dvorak intensity estimates from TAFB and SAB support keeping the initial intensity at 40 kt. The environment appears conducive for Norbert to strengthen over warm waters with low vertical wind shear. Despite this, most of the global and hi-res dynamical models do not strengthen Norbert, and in fact the HWRF and HMON both weaken the system over the next couple of days. Therefore, the consensus aids also do not indicate that the system will intensify. On the other end of the spectrum, the SHIPS guidance favors strengthening over the next couple of days and indicates that Norbert will be nearing hurricane strength within a few days. The latest NHC forecast remains above the consensus aids but below the SHIPS guidance, suggesting some gradual strengthening over the next 48 h, prior to the increase in shear. Norbert continues to move northwestward at 6 kt, steered by a weakening mid-level ridge centered over southern Mexico. The steering currents are forecast to collapse by tonight, and the cyclone is expected to meander through the middle of the week. By late this week, a weak mid-level ridge should build north of the cyclone which would result in a slow west-northwestward motion. Due to the weak steering flow, there is a larger than normal spread in the track guidance. The latest NHC forecast remains close to the consensus aids, and is slightly faster then the previous forecast at days 3-5. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 14.2N 106.6W 40 KT 45 MPH 12H 07/0000Z 14.4N 106.8W 45 KT 50 MPH 24H 07/1200Z 14.5N 106.8W 50 KT 60 MPH 36H 08/0000Z 14.7N 106.8W 50 KT 60 MPH 48H 08/1200Z 14.8N 106.8W 55 KT 65 MPH 60H 09/0000Z 15.0N 107.1W 55 KT 65 MPH 72H 09/1200Z 15.2N 107.8W 55 KT 65 MPH 96H 10/1200Z 15.7N 109.3W 55 KT 65 MPH 120H 11/1200Z 16.1N 110.4W 55 KT 65 MPH $$ Forecaster Latto

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Hurricane Delta Forecast Discussion Number 7

2020-10-06 10:57:45| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Tue Oct 06 2020 000 WTNT41 KNHC 060857 TCDAT1 Hurricane Delta Discussion Number 7 NWS National Hurricane Center Miami FL AL262020 500 AM EDT Tue Oct 06 2020 Delta has maintained a very deep central dense overcast during the past several hours, with overshooting cloud-top temperatures to -90C, and perhaps hints of an eye trying to emerge. On the last pass through the center, the Air Force plane reported a 4-mb pressure fall in one hour to 968 mb, with believable SFMR values of 80-85 kt. Thus, the initial wind speed is set to 85 kt. The hurricane is in the midst of a very impressive rapid intensification episode, having strengthened over 50 kt during the past 24 hours. I honestly don't see much that will stop it until it reaches Yucatan, due to low vertical wind shear, high deep-layer moisture, and the very warm and deep waters of the northwestern Caribbean. This is also supported by SHIPS rapid intensification probabilities that are well above 50 percent for most categories. Thus, the intensity forecast is raised to 115 kt near Yucatan landfall, closest to the HWRF forecast model, which has been a good performer this year, especially after ingesting NOAA radar data. Some weakening is expected due to land interaction, but conditions look ripe for re-intensification over the Gulf of Mexico. Almost all the guidance is higher, now showing Delta reaching category 4 status in the 2-to-3 day time frame, and the new NHC intensity forecast reflects this likelihood. However, an increase in southwesterly shear and cooler shelf waters near the northern Gulf coast should promote weakening, and little change has been made to the intensity forecast near landfall. Delta is moving much faster this morning to the west-northwest, with the latest estimates at about 13 kt. A strengthening mid-level ridge across Florida should steer the hurricane to the west-northwest or northwest during the next couple of days. Likely because of the deterioration of Gamma, model guidance is showing less poleward motion before Yucatan, and the official track is shifted to the west for the first day or so. Over the Gulf of Mexico, Delta should slow down and turn northward ahead of a trough moving eastward across Texas in a few days. Model guidance has again shifted westward, like the last cycle, and the official forecast is trended in that direction. However, it remains slightly east of the model consensus, due to a notable westward bias in some of the guidance during this hurricane season. Users are reminded to not focus on the details of the track or intensity forecasts, as the average 4-day track error is around 150 miles and the average 4-day intensity error is close to 15 mph. Key Messages: 1. Extremely dangerous storm surge and hurricane conditions are expected within portions of the northern Yucatan Peninsula of Mexico beginning tonight, and a Hurricane Warning is in effect. 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 and flash flooding will increase across portions of the central Gulf Coast, Tennessee Valley, and southeastern United States as Delta moves inland later this week. 3. Delta is forecast to approach the northern Gulf Coast late this week as a hurricane. While there is large uncertainty in the track and intensity forecasts, there is a significant risk of dangerous storm surge, wind, and rainfall hazards along the coast from Louisiana to the western Florida Panhandle beginning Thursday night or Friday. Residents in these areas should ensure they have their hurricane plan in place and monitor updates to the forecast of Delta. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 17.5N 81.3W 85 KT 100 MPH 12H 06/1800Z 18.7N 83.1W 100 KT 115 MPH 24H 07/0600Z 20.4N 85.8W 115 KT 130 MPH 36H 07/1800Z 21.8N 88.5W 105 KT 120 MPH 48H 08/0600Z 23.0N 90.4W 110 KT 125 MPH 60H 08/1800Z 24.2N 91.5W 115 KT 130 MPH 72H 09/0600Z 25.8N 92.0W 110 KT 125 MPH 96H 10/0600Z 29.8N 91.1W 85 KT 100 MPH...INLAND 120H 11/0600Z 34.0N 88.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake

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Tropical Storm Norbert Forecast Discussion Number 3

2020-10-06 10:53:46| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Tue Oct 06 2020 000 WTPZ44 KNHC 060853 TCDEP4 Tropical Storm Norbert Discussion Number 3 NWS National Hurricane Center Miami FL EP192020 300 AM MDT Tue Oct 06 2020 Deep convection has persisted overnight in association with former Tropical Depression Nineteen-E, forming a well-defined central dense overcast over the center. Additionally, a 0448 UTC ASCAT-B overpass showed a compact, circular wind field with at least 35-40 kt in the eastern semicircle of the system. Thus, the initial intensity has been raised to 40 kt, and the depression has been upgraded to Tropical Storm Norbert. Norbert is presently moving northwestward at 6 kt, steered by a weakening mid-level ridge centered over southern Mexico. The storm is expected to slow down later today as the steering currents collapse, and Norbert will likely meander offshore for several days before resuming a slow west-northwestward motion late in the forecast period. There remains above average spread in the track guidance given the weak steering flow, and the NHC track forecast lies fairly close to the consensus aids. Norbert is a compact storm over very warm waters, and the limited deep-layer shear it is experiencing should allow for steady strengthening over the next couple of days. The global guidance continues to struggle with this small storm, so the latest NHC intensity forecast trends well above the consensus aids and closer to the statistical-dynamical SHIPS guidance. Given the very favorable environmental conditions, it is certainly possible that Norbert could intensify even more than forecast. By day 3 and beyond, vertical wind shear is expected to increase, which could cause the storm's intensity to level off through the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 13.7N 106.2W 40 KT 45 MPH 12H 06/1800Z 14.0N 106.5W 45 KT 50 MPH 24H 07/0600Z 14.1N 106.7W 50 KT 60 MPH 36H 07/1800Z 14.3N 106.7W 55 KT 65 MPH 48H 08/0600Z 14.5N 106.7W 55 KT 65 MPH 60H 08/1800Z 14.7N 106.8W 55 KT 65 MPH 72H 09/0600Z 14.9N 107.3W 55 KT 65 MPH 96H 10/0600Z 15.0N 108.0W 55 KT 65 MPH 120H 11/0600Z 15.5N 109.0W 55 KT 65 MPH $$ Forecaster Reinhart/Stewart

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Tropical Storm Marie Forecast Discussion Number 29

2020-10-06 10:51:47| National Hurricane Center (East Pacific)

Issued at 1100 PM HST Mon Oct 05 2020 000 WTPZ43 KNHC 060851 TCDEP3 Tropical Storm Marie Discussion Number 29 NWS National Hurricane Center Miami FL EP182020 1100 PM HST Mon Oct 05 2020 A 6/0630Z ASCAT-B scatterometer overpass indicated that Marie has refused to weaken despite the deep convection being severely sheared to the northeast of the low-level center. A solid area of 40-kt was present northwest through northeast of the center, with a couple of 45-kt vectors present. However, the 45-kt vectors look like they could have been rain enhanced, so the initial intensity remains at 40 kt for this advisory. The initial motion estimate is 300/08 kt. There are no significant changes to the previous forecast track or reasoning. Marie is expected to move slowly west-northwestward along the southern periphery of a deep-layer ridge for the next 24 hours or so, during which time the cyclone will gradually spin down and become more vertically shallow. Thereafter, and continuing until dissipation occurs, a more westward motion is anticipated when the shallow system will be steered by the low-level easterly tradewind flow. The new NHC forecast track is similar to but a tad north of the previous advisory track, and lies near the middle of the tightly packed consensus aids. Although Marie has managed to survive some horrendous southwesterly vertical wind of at least 30 kt, the cyclone is not long for this world due to the shear increasing further while the cyclone moves over sub-25 deg C sea-surface temperatures for the next few days. These very unfavorable environmental conditions should result in all convection being stripped away by late Tuesday morning, causing Marie to degenerate into a 35-kt post-tropical cyclone. Further weakening is anticipated, with Marie becoming a remnant low by Tuesday night and dissipating by late Friday or Saturday over the far western portion of the eastern Pacific basin. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 21.7N 134.3W 40 KT 45 MPH 12H 06/1800Z 22.2N 135.5W 35 KT 40 MPH...POST-TROPICAL 24H 07/0600Z 22.7N 136.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 07/1800Z 23.0N 137.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 08/0600Z 23.2N 138.6W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 08/1800Z 23.1N 139.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 09/0600Z 23.2N 140.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 10/0600Z...DISSIPATED $$ Forecaster Stewart

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