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Tropical Storm Nate Forecast Discussion Number 7

2017-10-06 04:51:54| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Thu Oct 05 2017 000 WTNT41 KNHC 060251 TCDAT1 Tropical Storm Nate Discussion Number 7 NWS National Hurricane Center Miami FL AL162017 1100 PM EDT Thu Oct 05 2017 Nate's center has been moving northwestward across eastern Honduras, but it is just about to reach the waters of the northwestern Caribbean Sea. Despite moving over land for the past 12-15 hours, the cyclone appears to have a relatively intact and well-defined inner core. Deep convection has actually been increasing over the center, and recent 85-GHz microwave data showed at least some form of a convective ring. Given these signs, the maximum winds are being held at 35 kt. An Air Force Reserve Hurricane Hunter aircraft will be investigating Nate during the next several hours to get a better handle on the storm's intensity and structure. Nate has been moving northwestward while crossing Nicaragua and Honduras, and the initial motion estimate is 325/10 kt. The storm is currently embedded within a broad Central American gyre, and it should swing north-northwestward on the east side of this gyre during the next 36 hours. After 36 hours, Nate should turn northward and then northeastward along the western periphery of a mid-tropospheric high centered off the southeastern U.S. coastline. Compared to yesterday at this time, the track models have come into much better agreement, and all the reliable models take Nate's center across the northeastern portion of the Yucatan peninsula in 24 hours and then across the U.S. central Gulf coast between 48 and 60 hours. Because of this tight clustering, there are no notable cross-track changes in the NHC forecast. Speed-wise, however, the updated official forecast is a bit faster than the previous one and has caught up to the various consensus aids. Due to low shear and very high oceanic heat content in the northwestern Caribbean Sea, Nate should at least steadily strengthen once it moves offshore, especially since it appears to have a well-defined inner core. Rapid intensification is still not out of the question, and Nate could be near hurricane intensity by the time it reaches the Yucatan coast in about 24 hours. Land interaction with the Yucatan peninsula could cause a brief hiatus in the strengthening trend, but conditions should be conducive for additional intensification while Nate is over the Gulf of Mexico. Overall, the intensity models have not changed much on this cycle, and the NHC forecast still calls for a 48-hour intensity of 70 kt, which is at the upper end of the guidance between HWRF and HCCA. As mentioned before, Nate could strengthen further in the time between the 48-hour position and when it crosses the U.S. Gulf coast. KEY MESSAGES: 1. Heavy rainfall is the main threat from Nate in portions of Central America, with life-threatening flash flooding and mud slides possible in portions of Nicaragua, Honduras, Costa Rica, Panama, and Belize through Friday night. 2. Nate could be near hurricane intensity when it approaches the Yucatan Peninsula late Friday, bringing direct impacts from wind, storm surge, and heavy rainfall. A tropical storm warning and a hurricane watch are in effect for a portion of this area, and life-threatening flash flooding is also possible. 3. Nate is forecast to reach the northern Gulf Coast this weekend as a hurricane, and the threat of direct impacts from wind, storm surge, and heavy rainfall is increasing from Louisiana through the western Florida Panhandle. Hurricane and tropical storm watches, as well as a storm surge watch, have been issued for a portion of the northern Gulf Coast, and residents in these areas should monitor the progress of Nate, heeding any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 06/0300Z 15.8N 84.7W 35 KT 40 MPH...INLAND 12H 06/1200Z 17.8N 85.6W 40 KT 45 MPH...OVER WATER 24H 07/0000Z 20.8N 87.1W 50 KT 60 MPH...INLAND 36H 07/1200Z 24.3N 89.1W 60 KT 70 MPH...OVER WATER 48H 08/0000Z 27.5N 90.2W 70 KT 80 MPH 72H 09/0000Z 33.7N 87.9W 45 KT 50 MPH...INLAND 96H 10/0000Z 40.0N 79.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 11/0000Z 43.0N 68.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg

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Tropical Storm Nate Forecast Discussion Number 6

2017-10-05 22:45:51| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Thu Oct 05 2017 000 WTNT41 KNHC 052045 TCDAT1 Tropical Storm Nate Discussion Number 6 NWS National Hurricane Center Miami FL AL162017 500 PM EDT Thu Oct 05 2017 The center of Nate is now over eastern Honduras, and the cloud pattern has lost some organization since the last advisory due to passage over land. In addition, recent ASCAT overpasses suggest that there are no tropical-storm-force winds outside of the coastal waters of Nicaragua and Honduras. However, surface observations indicate that the central pressure remains near 1000 mb, and based on this the initial intensity remains a possibly generous 35 kt. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate Nate as it emerges from the northern coast of Honduras around 0300 UTC. Analyses from CIMSS at the University of Wisconsin suggest that Nate is currently experiencing about 20 kt of southwesterly vertical wind shear, which is more than suggested by the SHIPS model. The large-scale models are in good agreement that this shear should diminish during the next 12-24 h, leaving Nate in an favorable environment for strengthening. One change in the models from the previous advisory is that the GFS now shows more development as Nate crosses the Gulf of Mexico. The new intensity forecast shows little change during the first 12 h due to the shear and land interaction, then it calls for steady intensification though landfall on the northern Gulf Coast. After landfall, Nate should weaken as it traverses the eastern United States. It should be noted that while the forecast shows a peak intensity of 70 kt at 48 h, Nate is expected to continue to strengthen between 48 h and landfall and thus is likely to be stronger than 70 kt. It should also be noted that SHIPS Rapid Intensification Index values remain quite high, and any period of rapid intensification would lead to Nate being stronger than currently forecast. The initial motion is now 330/9. A combination of a large cyclonic gyre over Central America, a trough of low pressure moving westward across the Gulf of Mexico, and a building subtropical ridge over the western Atlantic should steer Nate generally north-northwestward with an increase in forward speed during the next 48 h or so, followed by a turn toward the north as the storm reaches the western end of the ridge. The guidance is in decent agreement on the direction of motion, but there remains disagreement on the speed despite a continued trend toward a faster motion. The new forecast track is similar to the direction of the previous track, but again shows a faster forward speed that now has the center near the northeastern Yucatan Peninsula in 24-36 h and near the northern Gulf Coast in 60-72 h. After the Gulf Coast landfall, Nate or its remnants are expected to recurve northeastward upon encountering the mid-latitude westerlies. KEY MESSAGES: 1. Heavy rainfall is the main threat from Nate in portions of Central America, with life-threatening flash flooding and mud slides possible in portions of Nicaragua, Honduras, Costa Rica, Panama, and Belize through Friday night. 2. Nate is forecast to be near hurricane intensity when it approaches the Yucatan Peninsula late Friday, bringing direct impacts from wind, storm surge, and heavy rainfall. A tropical storm warning and a hurricane watch are in effect for a portion of this area and life-threatening flash flooding is also possible. 3. Nate is forecast to reach the northern Gulf Coast this weekend as a hurricane, and the threat of direct impacts from wind, storm surge, and heavy rainfall is increasing from Louisiana through the Florida Panhandle. A hurricane watch and storm surge watch will likely be issued for portions of the northern Gulf Coast tonight or Friday morning, and residents in these areas should monitor the progress of Nate and heed any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 14.9N 84.3W 35 KT 40 MPH...INLAND 12H 06/0600Z 16.5N 84.9W 35 KT 40 MPH...OVER WATER 24H 06/1800Z 19.2N 86.1W 45 KT 50 MPH 36H 07/0600Z 22.3N 87.9W 55 KT 65 MPH 48H 07/1800Z 25.6N 89.5W 70 KT 80 MPH 72H 08/1800Z 31.5N 89.5W 50 KT 60 MPH...INLAND 96H 09/1800Z 38.0N 81.5W 25 KT 30 MPH...INLAND 120H 10/1800Z 41.5N 72.0W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Beven

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Tropical Storm Nate Forecast Discussion Number 5

2017-10-05 16:47:49| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Thu Oct 05 2017 000 WTNT41 KNHC 051447 TCDAT1 Tropical Storm Nate Discussion Number 5 NWS National Hurricane Center Miami FL AL162017 1100 AM EDT Thu Oct 05 2017 The cloud pattern associated with Tropical Depression Sixteen increased in organization after the last advisory, with the formation of a ragged central convective feature and outer banding in the northeastern semicircle. In addition, data from the Colombian radar at San Andres showed a partial eyewall, and surface observations from Puerto Cabezas, Nicaragua, included a pressure of 1001 mb outside of the center. Based on these data, the initial intensity has been increased to 35 kt, and the depression has been upgraded to Tropical Storm Nate. The center of Nate is now inland over northeastern Nicaragua, and little change in strength is expected until the center moves over the northwestern Caribbean Sea. After that, a combination of warm sea surface temperatures and light shear should allow for at least steady strengthening. However, the guidance is producing mixed signals despite a favorable-looking environment. The Rapid Intensification Index of the SHIPS model is showing high chances of rapid intensification, with better than a 50 percent chance of 25 kt of strengthening in the next 24 h and nearly a 50 percent chance of 65 kt of strengthening in 72 h. On the other side, the GFS and Canadian models show only modest development and keep the cyclone as a tropical storm until it reaches the northern Gulf coast. Given the environment, the intensity forecast leans towards the high end of the guidance envelope and calls for Nate to become a hurricane in about 48 h and reach the northern Gulf Coast as a hurricane. The initial motion is 325/8. A combination of a large cyclonic gyre over Central America, a trough of low pressure moving westward across the Gulf of Mexico, and a building subtropical ridge over the western Atlantic should steer Nate generally north-northwestward with an increase in forward speed during the next 72 h. While the guidance is in better agreement on the direction that Nate should move, there remains disagreement on the speed despite an overall trend toward a faster motion. The new forecast track is similar to the direction of the previous track, but shows a faster forward speed that has the center near the northeastern Yucatan Peninsula in about 36 h and near the northern Gulf Coast in about 72 h. After the Gulf Coast landfall, Nate or its remnants are expected to recurve northeastward upon encountering the mid-latitude westerlies. KEY MESSAGES: 1. Heavy rainfall is the main threat from Nate in portions of Central America, with life-threatening flash flooding and mud slides possible in portions of Nicaragua, Honduras, Costa Rica, Panama, and Belize through Friday night. 2. Nate is forecast to be near hurricane intensity when it approaches the Yucatan Peninsula late Friday, bringing direct impacts from wind, storm surge, and heavy rainfall. A tropical storm warning and a hurricane watch are in effect for a portion of this area and life-threatening flash flooding is also possible. 3. Nate is forecast to reach the northern Gulf Coast this weekend as a hurricane, and the threat of direct impacts from wind, storm surge, and heavy rainfall is increasing. However, it is too early to specify the exact timing, location, or magnitude of these impacts. Residents along the Gulf Coast from Louisiana through the Florida Panhandle should monitor the progress of Nate and heed any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 14.3N 83.7W 35 KT 40 MPH...INLAND 12H 06/0000Z 15.6N 84.3W 35 KT 40 MPH...INLAND 24H 06/1200Z 18.1N 85.4W 45 KT 50 MPH...OVER WATER 36H 07/0000Z 20.8N 86.8W 55 KT 65 MPH 48H 07/1200Z 23.7N 88.1W 65 KT 75 MPH 72H 08/1200Z 29.5N 89.5W 70 KT 80 MPH 96H 09/1200Z 36.0N 85.0W 30 KT 35 MPH...INLAND 120H 10/1200Z 41.5N 76.5W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Beven

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Tropical Depression Sixteen Forecast Discussion Number 4

2017-10-05 10:51:15| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Thu Oct 05 2017 000 WTNT41 KNHC 050851 TCDAT1 Tropical Depression Sixteen Discussion Number 4 NWS National Hurricane Center Miami FL AL162017 500 AM EDT Thu Oct 05 2017 Deep convection associated with the depression has increased over the eastern portion of the circulation overnight, however there has only been a slight increase in overall banding. Subjective Dvorak intensity estimates suggest that the depression is near tropical-storm strength, but with the center located near the western edge of the deep convection the cyclone is kept as a 30-kt tropical depression for this advisory. The intensity forecast remains quite uncertain due to expected land interaction today, and possibly again in about 48 hours when the system passes near the Yucatan peninsula. The depression could still become a tropical storm before the center moves over northeastern Nicaragua and eastern Honduras later today. After the cyclone moves north of Honduras, it will traverse the warm waters of the northwestern Caribbean Sea, where the upper-level environment is also forecast to be conducive for strengthening. However, the amount of strengthening is likely to depend on the structure of the inner core after it crosses land. The intensity models have continued their downward trend, but the NHC forecast remains near the higher side of the guidance due to these favorable conditions and persistence from the previous advisory. Some additional strengthening is possible while the system moves over the southern and central Gulf of Mexico, and the NHC intensity forecast brings the system to hurricane strength within 72 hours. This is in best agreement with the SHIPS intensity model. The depression is moving northwestward or 315/6 kt. The cyclone is forecast to move northwestward to north-northwestward during the next day or two around the western side of a ridge the extends from near the southeastern Bahamas southwestward into the central Caribbean Sea. By the weekend, a large mid- to upper-level ridge is forecast to build off the coast of the southeastern United States, and this should steer the cyclone north-northwestward at a faster forward speed. After 72 hours, the system is expected to recurve around the northwestward side of the ridge. The track guidance is in better agreement this cycle with the latest runs of the ECMWF and UKMET models shifting westward, closer to the previous GFS and HWRF iterations. This has required a fairly substantial westward shift in the NHC forecast track at 72 h and beyond. KEY MESSAGES: 1. The depression is forecast to strengthen and bring tropical storm conditions to portions of Nicaragua and Honduras through early Friday. Heavy rainfall could produce life-threatening flash flooding and mud slides in portions of Nicaragua, Honduras, Costa Rica, and Panama through Friday night. 2. The system could be near hurricane intensity when it approaches the Yucatan Peninsula late Friday, bringing direct impacts from wind, storm surge, and heavy rainfall, and a hurricane watch is in effect for a portion of this area. 3. The system is forecast to strengthen over the Gulf of Mexico and could affect portions of the northern Gulf Coast as a hurricane this weekend, with direct impacts from wind, storm surge, and heavy rainfall. However, it is too early to specify the timing, location, or magnitude of these impacts. Residents along the Gulf Coast from Louisiana through the Florida Panhandle should monitor the progress of this system and heed any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 13.3N 83.3W 30 KT 35 MPH 12H 05/1800Z 14.3N 83.9W 30 KT 35 MPH...INLAND 24H 06/0600Z 16.3N 84.8W 35 KT 40 MPH 36H 06/1800Z 19.0N 86.0W 45 KT 50 MPH 48H 07/0600Z 21.8N 87.4W 55 KT 65 MPH 72H 08/0600Z 27.8N 89.5W 65 KT 75 MPH 96H 09/0600Z 34.0N 86.5W 35 KT 40 MPH...INLAND 120H 10/0600Z 39.5N 79.0W 25 KT 30 MPH...POST-TROP/INLAND $$ Forecaster Brown

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Remnants of Ramon Forecast Discussion Number 5

2017-10-05 10:32:47| National Hurricane Center (East Pacific)

Issued at 400 AM CDT Thu Oct 05 2017 000 WTPZ44 KNHC 050832 TCDEP4 Remnants Of Ramon Discussion Number 5 NWS National Hurricane Center Miami FL EP192017 400 AM CDT Thu Oct 05 2017 Satellite data indicate that Ramon has degenerated into a trough of low pressure and that the shower activity near the center of circulation NHC was tracking has practically vanished. Since strong wind shear will prevail in this area, regeneration is not anticipated. This is the last advisory issued by the National Hurricane Center on this system. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 15.0N 102.5W 20 KT 25 MPH...REMNANT LOW 12H 05/1800Z...DISSIPATED $$ Forecaster Avila

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