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Tropical Storm Delta Forecast Discussion Number 5

2020-10-05 22:56:07| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Mon Oct 05 2020 000 WTNT41 KNHC 052055 TCDAT1 Tropical Storm Delta Discussion Number 5 NWS National Hurricane Center Miami FL AL262020 500 PM EDT Mon Oct 05 2020 Visible satellite imagery shows that the convective banding of Delta has continued to quickly improve since this morning. The primary convective band now wraps entirely around the center, with what appears to be a banding-type eye feature occasionally noted. There are some dry slots between the convective bands but those appear to be gradually filling in. A NOAA Hurricane Hunter aircraft currently collecting data in the storm environment found peak SFMR winds of 55 kt during its first pass through the center from northwest to southeast. The plane also reported a minimum pressure of 983 mb, much lower than previously estimated. The aircraft also observed an 18 nmi-wide-eye that was open to the west-northwest. Assuming that there are stronger winds yet to be sampled in the northeastern quadrant, the initial intensity has been raised to 60 kt. Delta is situated within a very conducive environment for strengthening. The storm will be moving over SSTs of 29-30 degrees Celsius and the vertical wind shear is forecast to remain 5 kt or less while Delta traverses the northwestern Caribbean. These conditions are expected to allow for rapid strengthening over the next 24 to 36 hours. The SHIPS Rapid Intensification Index gives a better than 50 percent chance of a 35-40 kt increase in wind speed over the next 24 hours. The NHC intensity forecast follow suit by calling for rapid intensification over the next day or so, and Delta is forecast to be a major hurricane when is passes near or over the northeastern portion of the Yucatan peninsula. Once the storm reaches the central Gulf of Mexico in 60-72 hours, increasing southwestern vertical wind shear and cooler shelf waters over the northern Gulf are likely to result in some reduction in wind speed as the system nears the northern Gulf coast. Although there is still significant uncertainty regarding Delta's intensity when it nears the northern Gulf coast, it is becoming increasing likely that the system will pose a significant wind and storm surge threat to a portion of that area. The center has jogged southward again this afternoon, which appears to be primarily due to the system organizing rather than a true storm motion. The initial motion estimate remains an uncertain 275/7 kt. Delta should begin moving west-northwestward this evening, and a west-northwestward to northwestward motion around the southwestern portion of a deep-layer ridge to its northeast is expected over the next couple of days. The more southward initial position and more ridging over the eastern Gulf of Mexico has resulted in a significant westward shift in the track envelope through the first 60-72 hours. The NHC has been adjusted in that direction, and this has required the issuance of a Hurricane Warning for the northeastern portion of the Yucatan peninsula of Mexico. After 72 hours, a mid- to upper-level trough is forecast to develop over Texas which should cause Delta to turn northward and then north-northeastward toward the northern Gulf Coast. Although the track forecast has not changed much during the latter portion of the period, there is more cross-track spread in the model guidance than before, which has increased the uncertainty regarding potential landfall and the timing of Delta's approach to the northern Gulf Coast. Key Messages: 1. Dangerous storm surge and hurricane conditions are expected within portions of the northern Yucatan Peninsula of Mexico and are possible in extreme western Cuba beginning Tuesday night, and a Hurricane Warning is in effect. 2. Heavy rainfall will affect portions of Jamaica, the Cayman Islands, western Cuba and the northern Yucatan Peninsula during the next few days. This rainfall could lead to significant flash flooding and mudslides. 3. Tropical storm conditions are expected in portions of the Cayman Islands beginning tonight or early Tuesday, and a Tropical Storm Warning is in effect. 4. 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 an increasing 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 05/2100Z 16.2N 79.4W 60 KT 70 MPH 12H 06/0600Z 17.1N 80.9W 75 KT 85 MPH 24H 06/1800Z 19.0N 83.5W 95 KT 110 MPH 36H 07/0600Z 21.0N 86.2W 105 KT 120 MPH 48H 07/1800Z 22.6N 88.7W 105 KT 120 MPH 60H 08/0600Z 23.7N 90.6W 105 KT 120 MPH 72H 08/1800Z 24.8N 91.5W 95 KT 110 MPH 96H 09/1800Z 28.5N 91.5W 85 KT 100 MPH 120H 10/1800Z 33.0N 89.0W 40 KT 45 MPH...INLAND $$ Forecaster Brown

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Tropical Storm Marie Forecast Discussion Number 27

2020-10-05 22:46:08| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Mon Oct 05 2020 000 WTPZ43 KNHC 052046 TCDEP3 Tropical Storm Marie Discussion Number 27 NWS National Hurricane Center Miami FL EP182020 200 PM PDT Mon Oct 05 2020 Deep convection associated with Maria has all but dissipated and what is left of it has been located over 120 n mi from the exposed low-level center of the cyclone since around 1400 UTC this morning. A recent ASCAT overpass shows the maximum winds have decreased to 43 kt as of 1800 UTC, and assuming weakening has continued since that time, 40 kt will be the initial advisory intensity. There are no reasons to believe that the deep convection will redevelop near the center of Marie, as the cyclone is forecast to remain in a hostile environment of 30 plus kt of wind shear, SSTs cooler than 25 degrees C, and a surrounding dry and stable airmass. Therefore, Maria is expected to be declared a remnant low by tonight. The remnant low should gradually spin down and open into a trough by late this week. Marie continues to move west-northwestward at about 8 kt around a mid-level ridge to its north. A turn to the west-southwest is expected in a couple of days as low- mid-level ridging builds to the northwest of what's left of the cyclone. The latest NHC track forecast is little changed from the previous one, and is near the various track consensus forecasts. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 21.4N 132.7W 40 KT 45 MPH 12H 06/0600Z 21.8N 133.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 06/1800Z 22.5N 135.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 07/0600Z 23.0N 136.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 07/1800Z 23.4N 137.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 08/0600Z 23.3N 138.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 08/1800Z 23.1N 139.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 09/1800Z...DISSIPATED $$ Forecaster Latto

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Tropical Depression Gamma Forecast Discussion Number 14

2020-10-05 22:34:07| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Mon Oct 05 2020 000 WTNT45 KNHC 052033 TCDAT5 Tropical Depression Gamma Discussion Number 14 NWS National Hurricane Center Miami FL AL252020 400 PM CDT Mon Oct 05 2020 The last couple of legs of the Air Force Reserve reconnaissance aircraft mission and recent METOP-A and C scatterometer passes support lowering Gamma's initial intensity to 30 kt for this advisory. Conventional satellite imagery reveals that the cyclone has been devoid of deep convection for nearly 10 hours and is on its way to becoming a post-tropical remnant low. Strong southerly shear and a stable, relatively dry surrounding air mass should prevent any significant convective regeneration as the system approaches the northern coast of the northwestern Yucatan peninsula tomorrow. After the remnants of Gamma makes landfall, dissipation is likely to occur Wednesday as larger, Tropical Storm Delta approaches the Yucatan Channel. The initial motion is estimated to be southwestward, or 230/4 kt. A continued southwestward or west-southwestward motion is expected through Wednesday morning while moving inland over the northern Mexican State of Yucatan. The NHC forecast track is basically an update of this morning's package and is based on the various multi-model consensus aids. KEY MESSAGES: 1. Gamma is expected to produce areas of heavy rainfall through midweek over portions of southeast Mexico, including the Mexican states of Yucatan, Campeche, and Tabasco. This rainfall could result in areas of flash flooding. 2. Gusty winds are likely along portions of the northern coast of the Yucatan Peninsula later today through Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 22.1N 88.1W 30 KT 35 MPH 12H 06/0600Z 21.6N 88.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 06/1800Z 20.9N 89.6W 25 KT 30 MPH...POST-TROP/INLAND 36H 07/0600Z 20.0N 90.1W 20 KT 25 MPH...POST-TROP/INLAND 48H 07/1800Z...DISSIPATED $$ Forecaster Roberts

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Tropical Storm Delta Forecast Discussion Number 4

2020-10-05 16:53:31| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Mon Oct 05 2020 000 WTNT41 KNHC 051453 TCDAT1 Tropical Storm Delta Discussion Number 4 NWS National Hurricane Center Miami FL AL262020 1100 AM EDT Mon Oct 05 2020 The convective structure of Delta has continued to improve this morning. Earlier microwave data and early-light visible satellite imagery showed that the center of the tropical cyclone re-formed farther south within the area of deep convection. Since that time, banding has continued to increase around the southern and eastern portion of the circulation, and a small CDO-like feature has formed. The intensity has been set at 40 kt, which is a blend of the subjective Dvorak estimate from TAFB and objective satellite intensity estimates from UW/CIMSS. A NOAA Hurricane Hunter aircraft is scheduled to investigate the tropical storm this afternoon, which should provide a better assessment of the cyclone's intensity, structure, and wind field. With the earlier center re-formation, the initial motion estimate is a somewhat uncertain 280/6 kt. Delta is expected to resume a west-northwestward motion later today. A northwestward heading around the southwestern portion of a deep-layer ridge should begin tonight or Tuesday, and that general motion with some increase in forward speed is expected to continue through 60-72 hours. After that time, a broad mid- to upper-level trough is forecast to develop over the south-central United States, which should weaken the western portion of the ridge and cause Delta to turn northward toward the northern Gulf Coast. After day 4, Delta should begin to accelerate north-northeastward or northeastward ahead of the aforementioned trough. The new NHC track forecast has been adjusted to the south and west of the previous advisory during the first couple of days, primarily due to the recent center re-formation and more southward initial position. After that time, the NHC track is not much different than the previous forecast and lies near the center of the tightly clustered dynamical model envelope. Delta is forecast to traverse very warm waters over the northwestern Caribbean Sea and be in a very low vertical wind shear environment during the next couple of days. These conditions should allow for significant strengthening during that time, and the NHC intensity forecast is at or above the various intensity aids. It is somewhat surprising that the intensity aids were generally a little lower this cycle, but the expected low shear and SHIPS rapid intensification index support the higher than climatological rate of intensification. After 72 hours, increasing southwesterly shear and the cooler shelf waters over the northern Gulf are likely to induce some weakening later in the period. The updated NHC intensity forecast calls for a faster rate of intensification over the next 48-60 hours, but is similar to the previous advisory thereafter. Key Messages: 1. Tropical storm conditions are expected in the Cayman Islands beginning late today or tonight, and a Tropical Storm Warning is in effect. 2. Dangerous storm surge and hurricane conditions are expected in portions of western Cuba by Tuesday afternoon, and a Hurricane Warning is in effect. 3. Heavy rainfall will affect portions of Jamaica, the Cayman Islands, and western Cuba during the next few days. This rainfall could lead to significant flash flooding and mudslides. 4. 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 at these time ranges, there is an increasing risk of dangerous storm surge, wind, and rainfall hazards along the coast from Louisiana to the western Florida Panhandle. Residents in these areas should monitor the progress of Delta and check for updates to the forecast during the week. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 16.4N 78.6W 40 KT 45 MPH 12H 06/0000Z 17.1N 79.6W 50 KT 60 MPH 24H 06/1200Z 18.7N 81.7W 60 KT 70 MPH 36H 07/0000Z 20.8N 84.3W 75 KT 85 MPH 48H 07/1200Z 22.8N 86.8W 85 KT 100 MPH 60H 08/0000Z 24.6N 89.1W 90 KT 105 MPH 72H 08/1200Z 26.0N 90.7W 90 KT 105 MPH 96H 09/1200Z 28.8N 91.1W 85 KT 100 MPH 120H 10/1200Z 33.1N 88.2W 40 KT 45 MPH...INLAND $$ Forecaster Brown

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Tropical Storm Marie Forecast Discussion Number 26

2020-10-05 16:50:32| National Hurricane Center (East Pacific)

Issued at 500 AM HST Mon Oct 05 2020 000 WTPZ43 KNHC 051450 TCDEP3 Tropical Storm Marie Discussion Number 26 NWS National Hurricane Center Miami FL EP182020 500 AM HST Mon Oct 05 2020 The remains of the deep convection associated with Marie continues to get further displaced from the exposed low-level center due strong upper-level westerly winds, with the gap now over 100 n mi between those two features. The various satellite intensity estimates suggest that the current intensity may only be 45 kt. However, due to fair number of 55-kt wind vectors on the ASCAT overpass early this morning, the intensity is conservatively being lowered to 50 kt for this advisory. Marie is expected to weaken over the next few days in a hostile environment of 30 plus kt of wind shear, over SSTs cooler that 25 degrees C, surrounded by a dry and stable airmass. With the convection now displaced so far from the center, and no regeneration of convection near the center anticipated, Marie is now forecast to become a remnant low by Tuesday night. This could happen even sooner if the current trend continues. Marie continues to move west-northwestward at about 8 kt around a mid-level ridge to its north. A turn to the west is expected in a couple of days as the cyclone becomes a more shallow system. The latest NHC track forecast is little changed from the previous one, and is near the various track consensus forecasts. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 21.1N 131.9W 50 KT 60 MPH 12H 06/0000Z 21.5N 133.0W 40 KT 45 MPH 24H 06/1200Z 22.1N 134.5W 35 KT 40 MPH 36H 07/0000Z 22.7N 136.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 07/1200Z 23.1N 137.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 08/0000Z 23.3N 138.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 08/1200Z 23.3N 138.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 09/1200Z 22.9N 140.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 10/1200Z...DISSIPATED $$ Forecaster Latto

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