BMS Tropical Update 10/04/2017 9 AM CDT

By: - October 4th, 2017

Despite the lull in new activity since September 16, the hurricane season is not over yet. This is not a surprise, as even the very active year of 2005 had periods of inactivity. As I last talked about in my September 25 update, the next area to watch for tropical development is the southwest Caribbean Sea. Just as expected, the NHC is now expected to label an area of low pressure in the Southwest Caribbean Sea Tropical Depression 16 (TD 16) at 11 AM EDT.

 

The NHC is expected to send aircraft reconnaissance into this developing area of low pressure later today, and if they find strong enough winds within the embedded thunderstorm activity, it could become Tropical Storm Nate later today.

As I talked about back on September 18th, the Main Development Region (MDR) tends to shut down as October approaches and new named storm development becomes more likely to form in the western Caribbean. In fact, if you look at the landfall locations for all U.S. hurricanes during the month of October since 1851, the Gulf of Mexico coastline and Florida’s west coast have been heavily favored areas.

Landfall locations for all continental U.S. hurricanes during October since 1851. West coast of Florida gets hit fairly often. Source; CSU

Future Track of TD 16
There is growing consensus that TD 16  will track northward into the Gulf of Mexico this weekend. In fact, some of the guidance suggests a hurricane could be in the Gulf of Mexico by this weekend with a landfall as early as Sunday morning.  The model guidance is suggesting a landfall location across the eastern Gulf of Mexico, so the Texas coastline has a very low probability of landfall at this point. Florida’s panhandle has the highest probability, which goes along with the climatology shown above.

Last nights multi-model European, American, and Canadian ensemble, strike probabilities for TD 16.

It is too early to provide insured loss guidance, but we know that Hurricane Hermine caused $205 million in insured loss to the region last year.

Future Intensity of TD 16
The key to how intense TD 16  becomes will be how much land interaction it sees as it moves northward over the next few days. What’s more troublesome with the current ensemble guidance above is that many of the members are showing a track of free reign over very warm water with little land interaction.

The average sea surface temp in the area Nate is expected to develop is 84 °F a major concern for hurricane development.

The area Nate is developing is some of highest tropical cyclone heat potential in the world right now.

This would mean a stronger storm as it tracks northward. A major hurricane cannot be ruled out at this time, although most of the early guidance is keeping this area of low pressure from becoming anything more than a tropical storm or minimal hurricane as it tracks into the Gulf of Mexico this weekend.

However, the ingredients for rapid strengthening are there, with a low wind shear environment and plenty of ocean heat content and warm sea surface temperatures.

The other key to the future intensity at landfall might be just how strong the storm has become as it enters the Gulf of Mexico. Stronger hurricanes often tend to weaken just before landfall, as the shallow continental shelf allows for colder water upwelling ahead of a hurricane and deprives it of an important energy source. Lili 2002 is the most extreme example of this, where it went from Category 4 to Category 1 in only 12 hours. There are certainly exceptions to this rule though, such as Camille 1969, Eloise 1975 and Frederic 1979, which were all major hurricanes that strengthened right up until landfall.

If a weaker hurricane is in the Gulf of Mexico, however, strengthening is almost always common right up until landfall, much like we saw already this year with Harvey.

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