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Tropical Storm Nestor Forecast Discussion Number 7

2019-10-19 04:35:33| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Fri Oct 18 2019 000 WTNT41 KNHC 190235 TCDAT1 Tropical Storm Nestor Discussion Number 7 NWS National Hurricane Center Miami FL AL162019 1000 PM CDT Fri Oct 18 2019 The Air Force and NOAA Hurricane Hunters are investigating Nestor this evening, and they have found that the minimum pressure has dropped to 996 mb, 3 mb lower than this afternoon, but they have not found higher winds yet. Based on preliminary data from both aircraft, the initial wind speed remains 50 kt. The Air Force also reported that there is a lot of lightning occurring in the thunderstorms on Nestor's east side. Nestor remains a lopsided tropical storm, with very intense deep convection extending well to the east of the center with only small areas of convection near and to the west of the center. This asymmetric cloud pattern is due to strong westerly wind shear associated with a nearby shortwave trough. Doppler radar imagery indicates that rain bands are now spreading inland over much of the eastern portions of the Gulf coast, and surface observations show the winds increasing near the coast, but they are still not quite at tropical storm strength. Water vapor satellite images show that the shortwave trough is almost co-located with Nestor, which is likely part of the reason why the minimum pressure has fallen. Even though it is not explicitly reflected in the forecast, Nestor could strengthen a little before the storm makes landfall. However, significant intensification seems unlikely as the shortwave trough is expected to bypass the cyclone soon, leaving the storm in a less favorable environment of upper-level confluence and drier air. After landfall, weakening is forecast and the models suggest that Nestor should lose its tropical characteristics on Saturday when it tracks across the southeast U.S. The weaker extratropical cyclone is expected to dissipate or merge with a cold front in about 4 days. The tropical storm is moving quickly northeastward at about 20 kt. The models are in good agreement that this general motion should continue for the next couple of days, taking the center of the storm inland over the Florida Panhandle on Saturday morning and across portions of Georgia and the Carolinas later Saturday and Sunday. The weakening system is expected to slow down and turn eastward over the western Atlantic early next week before it merges with a cold front. The NHC track forecast is nudged to the west of the previous one to be in better agreement with the latest consensus models. Given the structure of Nestor, dangerous storm surge and tropical-storm-force winds will occur along a large portion of the Florida Gulf Coast well east of the track of Nestor's center through Saturday. Key Messages: 1. There is a danger of life-threatening storm surge inundation of up to 5 feet above ground level along the Florida Gulf Coast from Indian Pass to Clearwater Beach, where a Storm Surge Warning is in effect. Residents in these areas should follow advice given by local officials. 2. Tropical storm force winds are spreading across portions of the Florida Gulf Coast, where tropical storm warnings are in effect. Regardless of the exact track and intensity of the system, these winds will cover a large area, especially east of the center. 3. Isolated flash flooding is possible along the central and eastern Gulf Coast and Southeast United States coast into early Sunday morning. 4. Wind and coastal flooding hazards along the U.S. East Coast will be covered by non-tropical watches and warnings issued by local NWS offices, since the system is expected to lose its tropical characteristics after it moves inland along the Gulf Coast. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 28.5N 87.0W 50 KT 60 MPH 12H 19/1200Z 30.2N 85.2W 50 KT 60 MPH 24H 20/0000Z 32.7N 82.3W 35 KT 40 MPH...POST-TROPICAL 36H 20/1200Z 34.9N 78.2W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 21/0000Z 36.5N 73.7W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 22/0000Z 37.5N 67.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 23/0000Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Storm Octave Forecast Discussion Number 6

2019-10-19 04:33:35| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Fri Oct 18 2019 000 WTPZ43 KNHC 190233 TCDEP3 Tropical Storm Octave Discussion Number 6 NWS National Hurricane Center Miami FL EP182019 800 PM PDT Fri Oct 18 2019 Octave's convection has waxed and waned since the tropical storm formed yesterday, and it's once again trending upward. Convection redeveloped in the northwest quadrant of the cyclone during the past few hours, staving off remnant low status for now. The intensity remains 35 kt, based on earlier ASCAT data. The global models indicate that upper-level winds will become unfavorable for the continued maintenance of deep convection on Saturday, so Octave is still not expected to last much longer as a tropical cyclone. The new NHC forecast maintains Octave as a tropical storm for 12 more hours, but this could be generous. Once it becomes a remnant low, occasional disorganized patches of convection will probably be enough to maintain a weak low for at least a few more days, but it is not expected to make any kind of significant comeback. Octave has continued to move northward, now at 4 kt. The shallow tropical storm is caught between low-level southwesterly flow to its south and easterly trade-wind flow to its north, and the dynamical guidance is in extremely poor agreement on which flow regime will dominate the motion of the cyclone after it becomes post-tropical over the weekend. A few models (including the ECMWF and HMON) forecast that neither regime will dominate and Octave will move very little for the next 5 days. The overall model spread is over 600 miles by day 5, but I have no reason to favor any one track over the others at this point. Therefore, the official track forecast is largely unchanged and lies near the middle of the unusually wide guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 11.5N 126.6W 35 KT 40 MPH 12H 19/1200Z 11.9N 126.3W 35 KT 40 MPH 24H 20/0000Z 11.9N 126.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 20/1200Z 11.6N 125.6W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 21/0000Z 11.2N 125.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 22/0000Z 11.4N 126.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 23/0000Z 12.5N 126.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 24/0000Z 13.0N 125.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky

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Tropical Storm Octave Forecast Discussion Number 5

2019-10-18 22:33:00| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Fri Oct 18 2019 000 WTPZ43 KNHC 182032 TCDEP3 Tropical Storm Octave Discussion Number 5 NWS National Hurricane Center Miami FL EP182019 200 PM PDT Fri Oct 18 2019 Octave's deep convection dissipated earlier this morning, leaving a well-defined swirl of low clouds in visible satellite imagery. With the degradation of the cyclone's structure, recent ASCAT data revealed that maximum winds have decreased to 35 kt. A new small burst of convection is going up to the west of the center, but it's difficult to know if this convection will continue and if it will meet the organizational requirements for a tropical cyclone. The new NHC forecast leaves open the possibility that Octave could maintain tropical cyclone status for another 24 hours, but it's probably at least equally likely that the storm could degenerate into a remnant low tonight if convection doesn't increase substantially. Either way, dry air and increasing shear are expected to cause Octave's winds to continue decreasing for the next 24 hours, with the remnant low maintaining 25-kt winds through the end of the forecast period. Octave's motion has been northward, or 360/4 kt. This motion is likely to be suppressed within the next 12-24 hours as a low-level trough to the north drops southward, and Octave is expected to make a tight clockwise loop during the 5-day forecast period. The updated NHC track forecast is a little east of the previous forecast, moved in the direction of the multi-model consensus aids. However, it should be noted that by day 5, there is a 700 n mi spread between the easternmost HWRF model and the westernmost UKMET model, suggesting that there is quite a bit of uncertainty on exactly where Octave will end up. Fortunately, it is not likely to be a significant cyclone at that time. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 11.0N 126.6W 35 KT 40 MPH 12H 19/0600Z 11.6N 126.3W 30 KT 35 MPH 24H 19/1800Z 11.9N 125.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 20/0600Z 11.7N 125.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 20/1800Z 11.3N 125.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 21/1800Z 11.1N 125.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 22/1800Z 11.9N 125.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 23/1800Z 12.9N 125.7W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg

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Tropical Storm Nestor Forecast Discussion Number 6

2019-10-18 22:32:30| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Fri Oct 18 2019 000 WTNT41 KNHC 182032 TCDAT1 Tropical Storm Nestor Discussion Number 6 NWS National Hurricane Center Miami FL AL162019 400 PM CDT Fri Oct 18 2019 Nestor's structure has evolved quite a bit today. Since the release of the previous advisory, the center has become better defined based on data from aircraft, satellite, and surface observations, and on that basis, the system was classified as a tropical cyclone around 1800 UTC. Since that time, the center has become more separated from the area of deep convection to the east, consistent with 30-40 kt of deep-layer westerly shear analyzed by the SHIPS model and UW-CIMSS. The initial intensity remains 50 kt based on aircraft data and earlier ASCAT data. The mid/upper-level trough seen in water vapor imagery over southeastern Louisiana is beginning to impinge on Nestor, and the cloud pattern has become more lopsided. It would not be surprising to see Nestor take on a more subtropical appearance overnight, as the GFS and ECMWF show the upper trough becoming superimposed on the low-level circulation, with the pressure continuing to deepen and some increase in the peak winds noted in both those models. This is reflected in the 12-h intensity forecast of 55 kt. After that time, the upper-level pattern becomes less favorable and Nestor should weaken while it moves inland over the southeastern United States and becomes post-tropical. Gale-force winds are shown over the western Atlantic waters, but are not expected over land areas from 24 h onward. The global models show Nestor's circulation dissipating by 96 hours, and that is reflected in the NHC forecast. The initial motion estimate is 050/19, but remains somewhat uncertain given the recent formation of a better defined center. The track forecast reasoning remains unchanged, with Nestor expected to move quickly northeastward ahead of the approaching upper trough and moving inland over the Florida Panhandle early Saturday. The circulation center will move across the southeastern United States before moving back offshore after 48 hours with a slower east-northeastward to eastward motion shown late in the period before dissipation. The new NHC track forecast lies a little to the right of the previous and is close to the middle of the guidance envelope. It should be noted that dangerous storm surge and tropical storm force winds will occur along a large portion of the Gulf Coast well east of the track of Nestor's center. Key Messages: 1. There is a danger of life-threatening storm surge inundation of up to 5 feet above ground level beginning this evening along the Florida Gulf Coast from Indian Pass to Clearwater Beach, where a Storm Surge Warning is in effect. Residents in these areas should follow advice given by local officials. 2. Tropical storm force winds are likely later today and tonight along portions of the Florida Gulf Coast, where tropical storm warnings are in effect. Regardless of the exact track and intensity of the system, these winds will cover a large area, especially east of the center. 3. Isolated flash flooding is possible along the central and eastern Gulf Coast and Southeast United States coast from late tonight through Sunday. 4. Wind and coastal flooding hazards along the U.S. East Coast will be covered by non-tropical watches and warnings issued by local NWS offices, since the system is expected to lose its tropical characteristics after it moves inland along the Gulf Coast. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 27.0N 88.5W 50 KT 60 MPH 12H 19/0600Z 28.9N 86.2W 55 KT 65 MPH 24H 19/1800Z 31.1N 83.7W 35 KT 40 MPH...POST-TROPICAL 36H 20/0600Z 33.4N 80.3W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 20/1800Z 35.4N 75.9W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 21/1800Z 36.6N 68.6W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 22/1800Z...DISSIPATED $$ Forecaster Brennan

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Potential Tropical Cyclone Sixteen Forecast Discussion Number 5

2019-10-18 16:55:28| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Fri Oct 18 2019 000 WTNT41 KNHC 181455 TCDAT1 Potential Tropical Cyclone Sixteen Discussion Number 5 NWS National Hurricane Center Miami FL AL162019 1000 AM CDT Fri Oct 18 2019 The satellite presentation of the system features an area of very deep convection with cloud tops colder than -80C within the eastern part of a rather broad and elongated surface circulation seen in visible satellite imagery and data from an Air Force Reserve Hurricane Hunter aircraft. A NOAA Hurricane Hunter aircraft found flight-level winds as high as 72 kt and SFMR winds of 45-50 kt southeast of the ill-defined center, and based on these data the initial intensity is set to 50 kt. The NOAA aircraft also measured a pressure of around 1001 mb. While the cyclone has deepened, the circulation is still quite elongated and not well defined, so the system is maintained as a Potential Tropical Cyclone for now. The global models continue to indicate that the circulation will consolidate and the system will strengthen some during the next 12 hours or so, as the low-level circulation will be overtaken by an upper-level trough currently situated over southwest Louisiana. The system is still expected to become a tropical or subtropical storm later today, with the exact phase dependent on the timing of the circulation improving and the interaction with the upper trough. Once the system moves inland, it should become extratropical by 36 hours and slowly weaken once it moves offshore of the Carolinas by 72-96 hours before dissipating by day 5. The new NHC intensity forecast is adjusted upward from the previous one through 24 hours based on the initial intensity and allows for the possibility of at least some additional strengthening later today. The initial motion is a somewhat uncertain 055/19 given the lack of a well-defined center. The track model guidance remains in good agreement on the system moving quickly northeastward toward the northeastern Gulf Coast during the next 24 hours as it interacts with the upper trough. After moving inland, a northeastward motion is forecast to continue until after 48 hours, when an east- northeastward motion is expected, which will take the circulation offshore over the Atlantic by 72 hours. The new NHC track forecast is similar to, but a bit to the south of the previous one and is close to the various track consensus aids. Regardless of the exact evolution of the system, portions of the northeastern coast of the Gulf of Mexico will experience strong winds, locally heavy rains, and storm surge later today and Saturday. Similar impacts are expected across portions of the Atlantic coast of the southeastern United States Saturday and Sunday. Key Messages: 1. There is a danger of life-threatening storm surge inundation of up to 5 feet above ground level beginning later today along the Florida Gulf Coast from Indian Pass to Clearwater Beach, where a Storm Surge Warning is in effect. Residents in these areas should follow advice given by local officials. 2. Tropical storm force winds are likely later today and tonight along portions of the central and eastern Gulf Coast, where tropical storm warnings are in effect. Regardless of the exact track and intensity of the system, these winds will cover a large area, especially east of the center. 3. Isolated flash flooding is possible along the central and eastern Gulf Coast and the southeast United States coast through Saturday night. 4. Wind and coastal flooding hazards along the U.S. East Coast will be covered by non-tropical watches and warnings issued by local NWS offices, since the system is expected to lose any tropical characteristics after it moves inland along the Gulf Coast. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 25.9N 90.0W 50 KT 60 MPH...POTENTIAL TROP CYCLONE 12H 19/0000Z 27.8N 88.0W 55 KT 65 MPH...TROPICAL STORM 24H 19/1200Z 29.9N 85.5W 50 KT 60 MPH 36H 20/0000Z 32.2N 82.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 20/1200Z 34.4N 78.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 21/1200Z 37.0N 71.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 22/1200Z 37.0N 69.0W 25 KT 30 MPH...POST-TROP/EXTRATROP 120H 23/1200Z...DISSIPATED $$ Forecaster Brennan

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