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Tropical Storm Norbert Forecast Discussion Number 6

2020-10-07 04:38:35| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Tue Oct 06 2020 000 WTPZ44 KNHC 070238 TCDEP4 Tropical Storm Norbert Discussion Number 6 NWS National Hurricane Center Miami FL EP192020 900 PM MDT Tue Oct 06 2020 Norbert's satellite presentation has degraded slightly over the past several hours as its convective cloud tops have warmed compared to earlier today. The system may be feeling the effects of some weak westerly wind shear, as the coldest cloud tops are displaced somewhat to the east of the estimated low-level center position. Regardless, objective satellite estimates from UW-CIMSS and a T3.0 Dvorak classification from TAFB support holding the initial intensity at 45 kt with this advisory. Sea surface temperatures of 29 degrees Celsius and 10 kt or less of deep-layer vertical wind shear should support at least modest strengthening during the next 24 h or so. The latest SHIPS guidance indicates moderate southeasterly wind shear will develop over this small cyclone by Thursday and persist into the upcoming weekend. This should inhibit further intensification and may even cause Norbert to weaken. There is once again a fairly large spread in the intensity guidance, with the global models still struggling to capture this compact system and depicting steady weakening during the next few days. Meanwhile, SHIPS guidance maintains Norbert at tropical storm strength and even shows some gradual strengthening. Since the statistical-dynamical models have performed better with Norbert, the NHC intensity forecast once again trends above the consensus aids and closer to the SHIPS/LGEM guidance. The official forecast shows Norbert peaking as a 50-kt tropical storm on Wednesday, then weakening slightly on Thursday and leveling off through the weekend. Norbert is drifting slowly north-northwestward tonight. The storm is expected to remain nearly stationary over the next couple of days as distant Hurricane Delta over the northwestern Caribbean Sea weakens the mid-level ridge that had been steering Norbert. This weak steering environment could lead to some erratic storm motion until the ridge becomes re-established later this week, but the track guidance consensus suggests little movement during the next couple of days. By Friday night, the storm should begin moving slowly westward or west-northwestward, and the models are in better agreement with regards to this general storm motion at 72 h and beyond. The latest NHC track forecast follows the consensus aids more closely than any individual model solution. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 14.5N 106.9W 45 KT 50 MPH 12H 07/1200Z 14.6N 107.0W 50 KT 60 MPH 24H 08/0000Z 14.7N 107.0W 50 KT 60 MPH 36H 08/1200Z 14.7N 107.1W 50 KT 60 MPH 48H 09/0000Z 14.7N 107.3W 45 KT 50 MPH 60H 09/1200Z 14.8N 108.0W 45 KT 50 MPH 72H 10/0000Z 15.2N 108.9W 45 KT 50 MPH 96H 11/0000Z 16.0N 110.5W 45 KT 50 MPH 120H 12/0000Z 16.5N 112.5W 50 KT 60 MPH $$ Forecaster Reinhart/Berg

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Tropical Storm Marie Forecast Discussion Number 31

2020-10-06 22:36:59| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Tue Oct 06 2020 000 WTPZ43 KNHC 062036 TCDEP3 Tropical Storm Marie Discussion Number 31 NWS National Hurricane Center Miami FL EP182020 200 PM PDT Tue Oct 06 2020 Marie's center remains exposed, with limited shower activity displaced more than 110 n mi northeast of the center. Consequently, the system is poised to become a remnant low tonight if organized convection doesn't redevelop near the center of circulation. The initial intensity is lowered to 35 kt, and is in best agreement with a blend of the various satellite intensity estimates and in deference to this morning's scatterometer data which indicated numerous 40-kt winds. Marie should continue to gradually spin down during the 36 hours while moving west-northwestward over 24C sea surface temperatures and through an extremely inhibiting surrounding environment. Through the remaining portion of the period, the post-tropical remnant low should turn westward within the low-level easterlies and open up into a trough of low pressure Friday. Only a small along-track adjustment was made to the NHC forecast in order to agree more with the HFIP Corrected Consensus Approach model. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 22.4N 135.6W 35 KT 40 MPH 12H 07/0600Z 22.8N 136.4W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 07/1800Z 23.2N 137.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 08/0600Z 23.4N 138.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 08/1800Z 23.4N 139.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 09/0600Z 23.4N 139.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 09/1800Z...DISSIPATED $$ Forecaster Roberts

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Tropical Storm Norbert Forecast Discussion Number 5

2020-10-06 22:34:27| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Tue Oct 06 2020 065 WTPZ44 KNHC 062034 TCDEP4 Tropical Storm Norbert Discussion Number 5 NWS National Hurricane Center Miami FL EP192020 300 PM MDT Tue Oct 06 2020 A compact central dense overcast with cloud tops occasionally cooling to -80 degrees C has persisted over the center of Norbert throughout the day. A recent ASCAT overpass showed peak winds of 41 kt near the center of storm. However, due to the small size of the cyclone, the highest winds are likely not being sampled. Therefore, the initial intensity is being raised to 45 kt, and this is in good agreement with the latest Dvorak CI values from TAFB and SAB. Norbert is expected to remain in an environment of low vertical wind shear while over very warm waters for the next couple of days. Despite the positive environmental factors in the near term, model guidance is in poor agreement on the future intensity of Norbert. The spread in the forecast intensity has widened even further today, with most of the global and hi-resolution dynamical models weakening the system over the next few days, while the SHIPS and LGEM guidance favor slow strengthening. Since the SHIPS guidance has been the most accurate for Norbert's intensity thus far, the latest NHC forecast is close to, but just below the SHIPS guidance values through 48 h. After 48 h, the shear is expected to become moderate, and there are indications that subsidence will increase over the cyclone. These negative environmental factors should inhibit further intensification, and could cause the cyclone to weaken. The steering currents around Norbert are collapsing, as the mid-level ridge over southern Mexico dissipates in response to Hurricane Delta over the northwestern Caribbean Sea. Model tracks diverge by a few hundred miles in varying directions while the steering flow is weak. The consensus guidance is in between these solutions and shows very little movement for the next 72 h. By late this week, a weak mid-level ridge should build north of the cyclone, which would result in a slow west-northwestward to westward motion. The latest NHC track forecast remains close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 14.4N 106.6W 45 KT 50 MPH 12H 07/0600Z 14.5N 106.7W 50 KT 60 MPH 24H 07/1800Z 14.5N 106.7W 50 KT 60 MPH 36H 08/0600Z 14.5N 106.7W 55 KT 65 MPH 48H 08/1800Z 14.5N 106.7W 55 KT 65 MPH 60H 09/0600Z 14.5N 107.2W 50 KT 60 MPH 72H 09/1800Z 14.8N 108.0W 50 KT 60 MPH 96H 10/1800Z 15.5N 110.1W 50 KT 60 MPH 120H 11/1800Z 16.0N 112.0W 50 KT 60 MPH $$ Forecaster Latto

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Hurricane Delta Forecast Discussion Number 9

2020-10-06 22:34:27| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Tue Oct 06 2020 064 WTNT41 KNHC 062034 TCDAT1 Hurricane Delta Discussion Number 9 NWS National Hurricane Center Miami FL AL262020 500 PM EDT Tue Oct 06 2020 Shortly after the release of the 1500 UTC advisory package, the NOAA Hurricane Hunter aircraft measured a peak flight-level wind of 132 kt, and during its final passage through the northeast eyewall around 1700 UTC it reported a peak SFMR wind of 121 kt. The aircraft continued to report an extremely small 4-to-5-nmi-wide eye. The central pressure did level off somewhat on the final couple of penetrations, with the latest reported central pressure at 956 mb. The initial wind speed was raised to 120 kt on the earlier intermediate advisory, and has been set at 125 kt for this advisory. The next reconnaissance aircraft mission into the hurricane is scheduled for this evening. There has been no evidence of an outer eyewall from the aircraft reports or earlier radar imagery from Grand Cayman. As a result, some additional strengthening is likely to occur before Delta reaches the northeastern coast of the Yucatan peninsula late tonight or early Wednesday. The NHC intensity forecast is once again a little above the various intensity aids until landfall in Mexico. When the small inner core of Delta moves over land, weakening is expected, but warm waters and low vertical wind shear over the southern Gulf of Mexico should support re-strengthening, and a second peak in intensity is likely when Delta is over the central Gulf of Mexico in 48-60 hours. After that time, increasing southwesterly shear and the cooler shelf waters over the northern Gulf are expected to cause some reduction in wind speed. The global models, however, depict a significant increase in the size of Delta's wind field while it is over the Gulf of Mexico, which increases the spatial extent of the storm surge and wind threats for the northern Gulf coast. So regardless of Delta's final landfall intensity, the projected large size of the hurricane is likely to result in a significant storm surge and wind event for portions of the northern Gulf coast later this week. Delta has been moving steadily west-northwestward today at 300/15 kt. The track forecast reasoning remains unchanged from the previous advisory. A mid-level ridge over Florida and the northeastern Gulf of Mexico is expected to continue steering Delta west-northwestward during the next 36-48 hours. After that time, a developing trough over the south-central United States should cause Delta to turn northward, and by Friday the hurricane is forecast to begin accelerating northward or north-northeastward ahead of the trough. This motion will bring Delta onshore along the northern Gulf coast between 72 and 96 hours. The dynamical models continue to be tightly clustered through 48-72 hours with some increase in spread thereafter. The overall trend in the guidance has been slightly westward, and the new forecast has been adjusted accordingly and lies near the middle of the envelope. Supplemental upper-air balloon launches at 0600 and 1800 UTC have begun at upper-air sites across portions of the southeastern United States. In addition, a NOAA G-IV synoptic surveillance mission is in progress and should provide additional data for the 0000 UTC cycle of the dynamical models. 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 06/2100Z 18.9N 84.1W 125 KT 145 MPH 12H 07/0600Z 20.2N 86.1W 135 KT 155 MPH 24H 07/1800Z 21.8N 88.8W 105 KT 120 MPH 36H 08/0600Z 23.0N 91.1W 110 KT 125 MPH 48H 08/1800Z 24.4N 92.6W 115 KT 130 MPH 60H 09/0600Z 25.9N 93.2W 115 KT 130 MPH 72H 09/1800Z 28.0N 92.9W 110 KT 125 MPH 96H 10/1800Z 32.4N 90.9W 55 KT 65 MPH...INLAND 120H 11/1800Z 35.5N 87.3W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Hurricane Delta Forecast Discussion Number 8

2020-10-06 16:54:19| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Tue Oct 06 2020 000 WTNT41 KNHC 061454 TCDAT1 Hurricane Delta Discussion Number 8 NWS National Hurricane Center Miami FL AL262020 1100 AM EDT Tue Oct 06 2020 Satellite imagery and recent NOAA Hurricane Hunter aircraft data show that Delta is a very symmetric and compact hurricane. The aircraft reported a tiny 5-nmi-wide eye, which has also been seen in radar imagery from the Cayman Islands, and there is a hint of a pinhole eye in infrared satellite data. The central pressure has continued to fall, with the lastest center dropwindsonde data supporting a pressure of 955 mb. The plane has reported a peak flight-level winds of 109 kt, and believable SFMR winds of 102 kt. Therefore, the initial intensity is set at 100 kt, making Delta the third major hurricane of the 2020 Atlantic hurricane season. Delta has continued to rapidly strengthen over the past 24 hours, with an estimated 55-kt increase in wind speed between 1200 UTC Monday and 1200 UTC today. Environmental conditions of low vertical wind shear, deep warm waters, and sufficient mid-level moisture are expected to support additional rapid intensification through today, and the only reason that the strengthening could slow is if a difficult-to-predict eyewall replace cycle begins. The SHIPS Rapid intensification index continues to indicate a high likelihood of at least an additional 25-30 kt of intensity increase before the system reaches the northeastern portion of the Yucatan Peninsula. Given that, the NHC intensity forecast is above the various intensity aids and call for Delta to be an extremely dangerous category 4 hurricane when it nears the Yucatan. It could be stronger than indicated below since landfall is predicted to occur between the 12 and 24 h forecast points. Some reduction in intensity is likely when Delta moves over land, but the environmental conditions over the southern Gulf of Mexico are expected to support re-strengthening, and the NHC intensity forecast shows a second peak in 48-72 hours. As mentioned before, increasing southwesterly shear and cooler shelf waters near the northern Gulf coast are expected to cause some reduction in wind speed, but Delta is still expected to be a dangerous hurricane when it nears the northern Gulf coast. Delta is moving west-northwestward at about 14 kt. A mid-level ridge that extends westward across Florida and the northeastern Gulf of Mexico should continue to steer Delta west-northwestward to northwestward during the next couple of days. As the hurricane nears the western portion of the ridge it should slow down. By day three a developing trough over the south-central United States is expected to cause Delta to turn northward toward the northern Gulf coast. The track guidance is tightly clustered through 48 hours, but there is still a fair amount of spread thereafter regarding the timing and details of the northward turn. The ECMWF and its ensemble mean are well west of the bulk of the remainder of the guidance. The NHC track lies near the TVCA multi-model consensus which is close to a blend of the GFS, HWRF, UKMET ensemble mean. 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. 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 monitor updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 18.2N 82.6W 100 KT 115 MPH 12H 07/0000Z 19.4N 84.5W 120 KT 140 MPH 24H 07/1200Z 21.0N 87.2W 120 KT 140 MPH 36H 08/0000Z 22.3N 89.6W 105 KT 120 MPH 48H 08/1200Z 23.4N 91.3W 110 KT 125 MPH 60H 09/0000Z 24.6N 92.3W 115 KT 130 MPH 72H 09/1200Z 26.3N 92.5W 110 KT 125 MPH 96H 10/1200Z 30.5N 91.2W 70 KT 80 MPH...INLAND 120H 11/1200Z 34.5N 87.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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