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Tropical Depression Norbert Forecast Discussion Number 13

2020-10-08 22:33:20| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Thu Oct 08 2020 000 WTPZ44 KNHC 082033 TCDEP4 Tropical Depression Norbert Discussion Number 13 NWS National Hurricane Center Miami FL EP192020 300 PM MDT Thu Oct 08 2020 Norbert has a ragged and disorganized appearance, with asymmetrical convection bursting intermittently around the center. Satellite imagery suggests that the system is now experiencing some southeasterly shear. A recent ASCAT overpass sampled peak winds of 24 kt, so the advisory intensity will remain 25 kt. The current environment surrounding Norbert is not forecast to change much over the next few days. Therefore, only minor fluctuations in intensity are expected to occur during that time. By 72 h, model guidance is indicating that the cyclone should encounter a more stable atmosphere, which would limit convection and cause Norbert to weaken. The cyclone is forecast to degenerate into a remnant low devoid of deep convection by day 4, but it is possible that the deep convection could dissipate long enough for Norbert to be declared a remnant low before that time. Another plausible scenario is that Norbert's low level circulation dissipates and opens up into a surface trough later in the forecast period. The only change to the latest NHC forecast is that no further strengthening is indicated, which is agreement with every available intensity model except the SHIPS guidance. Norbert has barely budged since early this morning due to a lack of steering currents. A weak mid-level ridge is forecast to build to the northeast of the cyclone Friday through Saturday, which should cause Norbert to eventually move west-northwest to northwest. By Sunday, however, a mid-upper level low digging across northern Mexico should weaken the ridge, and the model guidance has trended toward Norbert once again meandering for a couple of days. By day 5, low-level ridging building to the northwest of Norbert should cause the shallow system to begin a westward motion. Due to the lack of run-to-run model consistency in the 3-5 day period, that portion of the track forecast is of low confidence. The NHC forecast track was changed little through 48 h, then is slower at 60-96 h to reflect the second collapse of the steering currents. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 13.1N 106.1W 25 KT 30 MPH 12H 09/0600Z 13.0N 106.2W 25 KT 30 MPH 24H 09/1800Z 13.3N 106.7W 25 KT 30 MPH 36H 10/0600Z 13.9N 107.3W 25 KT 30 MPH 48H 10/1800Z 14.5N 107.6W 25 KT 30 MPH 60H 11/0600Z 14.8N 107.6W 25 KT 30 MPH 72H 11/1800Z 14.9N 107.7W 25 KT 30 MPH 96H 12/1800Z 15.0N 107.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 13/1800Z 15.1N 109.6W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Latto

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Hurricane Delta Forecast Discussion Number 16

2020-10-08 16:54:12| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Thu Oct 08 2020 000 WTNT41 KNHC 081454 TCDAT1 Hurricane Delta Discussion Number 16 NWS National Hurricane Center Miami FL AL262020 1000 AM CDT Thu Oct 08 2020 Satellite imagery shows that Delta is better organized this morning, with the center well embedded in a cold central dense overcast and a hint of a eye developing in the overcast. Reports from Air Force Reserve and NOAA Hurricane hunter aircraft indicate that the central pressure has fallen to 968 mb inside a 35 n mi wide eye, along with flight-level and SFMR winds that support an initial intensity of 90 kt. The initial motion remains northwestward or 305/12 kt. The track forecast is reasonably straightforward. During the next 12-24 h, Delta should turn to the north between a mid- to upper-level ridge over the Florida Peninsula and eastern Gulf of Mexico and a mid- to upper-level level trough over the U.S. Southern Plains. This should be followed by a north-northeastward motion that is expected to bring the center near or over the northern Gulf coast, most likely in southwestern Louisiana, in about 36 h. After landfall, the cyclone should move northeastward through the Lower Mississippi and Tennessee Valleys along the southern edge of the mid-latitude westerlies until it dissipates. The track guidance is very tightly clustered in terms of direction, and the new forecast track has only minor tweaks from the previous one. Shear, sea surface temperature, and moisture conditions appear favorable for strengthening during the next 12-24 h or so, and based on this Delta is expected to regain major hurricane strength. Rapid intensification cannot be ruled out, although the various rapid intensification indices do not suggest a high chance, and the first 24 h of the forecast is already above the intensity guidance. The global models forecast strong southwesterly shear developing over the hurricane during the last 12 h before landfall, and based on this some weakening is forecast. Rapid weakening is expected after landfall, with Delta forecast to degenerate to a remnant low by 72 h and dissipate shortly after that. It should be noted that the NHC 1-2 day intensity forecasts are subject to errors of around 1 Saffir-Simpson category. Delta is expected to grow in size as it approaches the Louisiana coast. The NHC wind radii forecast again follows a consensus of the global and hurricane regional models. Key Messages: 1. Life-threatening storm surge is expected near and east of where Delta makes landfall on Friday, and a Storm Surge Warning is in effect from High Island, Texas, to Ocean Springs, Mississippi. The highest inundation of 7 to 11 feet is expected somewhere between Rockefeller Wildlife Refuge and Port Fourchon, Louisiana. Residents in the warning area should promptly follow advice given by local officials. The storm surge risk remains high despite the forecast decrease in intensity before landfall since Delta is expected to grow in size. 2. Hurricane-force winds are expected Friday afternoon and evening somewhere within the Hurricane Warning area between High Island, Texas, and Morgan City, Louisiana. Hurricane-force winds will also spread inland across portions of southern Louisiana near the path of Deltas center Friday evening and Friday night. 3. Significant flash flooding and minor to moderate river flooding are likely in parts of Louisiana Friday and Saturday, with additional flooding in portions of the central Gulf Coast into the Lower Mississippi Valley. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 24.0N 92.7W 90 KT 105 MPH 12H 09/0000Z 25.4N 93.6W 95 KT 110 MPH 24H 09/1200Z 27.5N 93.8W 100 KT 115 MPH 36H 10/0000Z 29.8N 93.1W 90 KT 105 MPH...ON THE COAST 48H 10/1200Z 32.4N 91.7W 45 KT 50 MPH...INLAND 60H 11/0000Z 34.0N 90.0W 30 KT 35 MPH...INLAND 72H 11/1200Z 35.6N 87.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 12/1200Z...DISSIPATED $$ Forecaster Beven

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Tropical Depression Norbert Forecast Discussion Number 12

2020-10-08 16:43:12| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Thu Oct 08 2020 000 WTPZ44 KNHC 081443 TCDEP4 Tropical Depression Norbert Discussion Number 12 NWS National Hurricane Center Miami FL EP192020 900 AM MDT Thu Oct 08 2020 Intermittent bursts of deep convection are maintaining the circulation of Norbert. First-light visible satellite imagery shows the latest burst over the northeastern potion of the cyclone with a partially exposed low-level center. The initial intensity is being held at 25 kt, and is supported by the latest Dvorak satellite intensity estimates from TAFB and SAB, as well as data from an earlier ASCAT overpass. The environment surrounding Norbert is not forecast to change much over the next few days, with perhaps some slight increase in the atmospheric moisture in about 24 h. Therefore, only minor fluctuations in intensity are expected to occur during that time. By 72 h, model guidance is indicating that the cyclone should encounter a more stable atmosphere, which should limit convection and cause Norbert to weaken. The cyclone is forecast to degenerate into a remnant low devoid of deep convection by day 4, but it is possible that the deep convection could dissipate long enough for Norbert to be declared a remnant low before that time. Norbert has been nearly stationary since the previous advisory, and very little motion is expected today due to a lack of steering currents. A mid-level ridge is forecast to slowly build to the northeast of the cyclone Friday through the weekend, which should cause Norbert to eventually move west-northwest to northwest. By late in the forecast period, the forecast track becomes quite uncertain, as there are now indications that whatever is left of Norbert may interact with a disturbance to its west. The latest NHC track forecast is little changed from the previous one through 72 h, but is left of that track beyond 72 h due to a shift in the consensus guidance. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 13.2N 106.2W 25 KT 30 MPH 12H 09/0000Z 13.0N 106.3W 25 KT 30 MPH 24H 09/1200Z 13.0N 106.7W 25 KT 30 MPH 36H 10/0000Z 13.4N 107.2W 30 KT 35 MPH 48H 10/1200Z 14.1N 107.8W 30 KT 35 MPH 60H 11/0000Z 14.9N 108.1W 30 KT 35 MPH 72H 11/1200Z 15.5N 108.4W 25 KT 30 MPH 96H 12/1200Z 15.8N 109.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 13/1200Z 15.9N 110.3W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Latto

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Tropical Depression Norbert Forecast Discussion Number 11

2020-10-08 10:44:08| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Thu Oct 08 2020 000 WTPZ44 KNHC 080843 TCDEP4 Tropical Depression Norbert Discussion Number 11 NWS National Hurricane Center Miami FL EP192020 300 AM MDT Thu Oct 08 2020 Norbert was very close to becoming a remnant low overnight. A recent burst of deep convection to the southeast of the partially exposed low-level center was sufficient to keep Norbert as a tropical depression for this advisory. Water vapor imagery indicates the depression is still battling dry mid-level air on the northern periphery of the circulation. The initial intensity has been lowered to 25 kt based on a 04 UTC ASCAT-B overpass that showed max winds of 25 kt in the southwest quadrant of Norbert. Norbert is presently drifting east-southeastward under weak steering currents, and the cyclone may continue meandering erratically for the next 6-12 h. Then, Norbert is forecast to move slowly west-southwestward or westward through 48 h. Thereafter, a mid-level ridge is expected to build to the north and northeast of Norbert, which should steer the system northwestward at a slightly faster speed. The NHC forecast track is shifted slightly to the right of the previous one based on the guidance consensus aids including TVCE and HCCA. Although drier mid-level air continues to impinge on the northern side of Norbert's circulation, the depression remains in an otherwise favorable environment of high oceanic heat content and light vertical wind shear. If Norbert can survive the slight increase in deep-layer shear depicted by the SHIPS guidance during the next 24 h, improving environmental conditions thereafter could allow Norbert to at least remain a depression for several days. Alternatively, moderate shear and additional dry air intrusions could cause Norbert to degenerate into a remnant low at almost any time. The NHC intensity forecast assumes the first scenario and keeps Norbert as a 25-30 kt depression for the next several days. By 96-120 h, GFS simulated satellite imagery suggests the cyclone will be devoid of convection as it moves into a drier mid-level environment. Thus, the official forecast depicts a transition to remnant low status by day 4. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 13.2N 106.3W 25 KT 30 MPH 12H 08/1800Z 13.0N 106.2W 25 KT 30 MPH 24H 09/0600Z 13.0N 106.5W 25 KT 30 MPH 36H 09/1800Z 13.2N 107.0W 30 KT 35 MPH 48H 10/0600Z 13.5N 107.6W 30 KT 35 MPH 60H 10/1800Z 14.4N 108.2W 30 KT 35 MPH 72H 11/0600Z 15.3N 108.6W 30 KT 35 MPH 96H 12/0600Z 16.0N 109.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 13/0600Z 16.5N 110.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Reinhart/Zelinsky

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Hurricane Delta Forecast Discussion Number 15

2020-10-08 10:33:07| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Thu Oct 08 2020 000 WTNT41 KNHC 080832 TCDAT1 Hurricane Delta Discussion Number 15 NWS National Hurricane Center Miami FL AL262020 400 AM CDT Thu Oct 08 2020 Satellite images indicate that Delta remains a well organized hurricane with a central dense overcast feature and curved bands beyond that. There is still no indication of an eye, however, in geostationary satellite images. The Air Force Hurricane Hunters were in Delta a few hours ago and toward the end of that mission, they reported maximum flight-level winds of 102 kt and SFMR winds of 77 kt. Based on a blend of this data, the initial intensity was increased to 85 kt at 0600 UTC. Since the cyclone appears to be generally steady in strength since that time, the wind speed is held at that value. Both the NOAA and Air Force Hurricane Hunters will be investigating Delta later today, and that data will help us assess its strength and structure. The track forecast reasoning is unchanged. Delta is currently moving northwestward at 13 kt on the southwestern periphery of an Atlantic subtropical ridge. The western portion of the ridge is expected to weaken later today as a trough moves eastward across the south-central United States. This change in the steering pattern should cause Delta to turn northward by late tonight and north-northeastward by Friday night. This motion should take the core of the hurricane to the Louisiana coast in a little more than 36 hours (sometime Friday afternoon or evening). After landfall, a turn to the northeast is forecast as a larger trough approaches Delta from the west. The models are in very good agreement, and the NHC track forecast is just an update of the previous one. Delta is expected to continue gradually strengthening during the next 24 hours while it remains over warm deep waters and in an environment of low wind shear and a high amount of moisture. Based on these favorable environmental conditions and the trend in the models, Delta is forecast to regain major hurricane status by tonight. Just prior to making landfall, the cyclone is forecast to level off in strength or weaken slightly as it moves over the cooler shelf waters and into somewhat less favorable atmospheric conditions. Rapid weakening is forecast after Delta moves inland. The intensity models are in fairly good agreement, and the NHC intensity forecast lies near the middle of the guidance envelope. It should be noted that the NHC 1-2 day intensity forecasts are subject to errors of around 1 Saffir-Simpson category. The aircraft and fairly recent scatterometer data indicate that Delta is gradually growing in size. This trend is expected to continue as Delta approaches the Louisiana coast. The NHC wind radii forecast follows a consensus of the global and hurricane regional models. 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. Significant 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 Mississippi Valley. As Delta moves farther inland, heavy rainfall is expected in the Ohio Valley and Mid-Atlantic this weekend. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 23.4N 91.8W 85 KT 100 MPH 12H 08/1800Z 24.6N 93.0W 95 KT 110 MPH 24H 09/0600Z 26.4N 93.7W 100 KT 115 MPH 36H 09/1800Z 28.8N 93.4W 90 KT 105 MPH 48H 10/0600Z 31.3N 92.4W 55 KT 65 MPH...INLAND 60H 10/1800Z 33.3N 90.9W 30 KT 35 MPH...INLAND 72H 11/0600Z 34.6N 89.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 12/0600Z...DISSIPATED $$ Forecaster Cangialosi

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