Update on Tropical Cyclone Nate

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.


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