2:30 PM Update | ***Tropical system over Gulf of Mexico to slam into Florida as likely first hurricane since 2005…Labor Day weekend weather in serious jeopardy in the Mid-Atlantic and Northeast US***

Impressive-looking tropical system (TD 9) lurking over the Gulf of Mexico; image courtesy NOAA/NASA

Overview
It has been a long time in the making and still has a long way to go.  First, this tropical wave of interest was dubbed “99L” as it slowly moved through the northern Caribbean Sea.  Then it became classified by NOAA as tropical depression (TD) #9 as it slowly continued on a path towards the southern Gulf of Mexico.  At 11am today, NOAA’s National Hurricane Center (NHC) has it still officially classified as “TD 9”, but I think it is likely to be upgraded to “tropical storm” status later today after another visit by NOAA's hurricane hunters aircraft (would be named Hermine).

TD 9 is likely to undergo intensification over the next 24-36 hours before making landfall along the Florida Panhandle sometime tomorrow night or early Friday.  In fact, it is likely that this system will reach hurricane status, in my opinion, before making landfall and, if so, this would be the first hurricane of any intensity to reach Florida since October 2005 and that would end an unprecedented streak in the record-keeping era that dates back to the middle 1800’s. Hurricane Wilma came ashore in southwestern Florida during late October of 2005 as a major hurricane and that was not only the last hurricane to hit Florida, but it was also the last major hurricane (i.e., category 3, 4 or 5) to strike U.S. soil in what is another on-going unprecedented streak.

The latest official track of the NOAA/National Hurricane Center.  TD 9 is likely to be on the western fringes of their forecast path; courtesy NOAA

Short-term outlook (Florida/SE US)

Multiple factors favor intensification of TD 9 over the next 24-36 hours.  First, sea surface temperatures throughout the Gulf of Mexico are quite warm and, in most areas, above-normal for this time of year at 85°F or higher.  Second, the upper-level outflow (i.e., divergence) has expanded to the north and northwest of the system and as TD 9 heads towards the entrance region of an upper-level (250 mb) jet, strengthening becomes more likely. Finally, wind shear is quite low in the vicinity of the tropical system and it should remain low during the next 24 hours or so and this too is favorable for intensification.  

Sea surface temperature anomalies with well above normal readings off the Mid-Atlantic and Northeast US coastlines; image courtesy Weather Bell Analytics

TD 9 has generally been meandering over the last several hours and its center is difficult to locate, but it should begin to make a turn to the north or northeast later today.  A deepening trough over the Southeast US should cause TD 9 to head northeast and then to begin acceleration in this direction by early tomorrow.   Heavy rain will inundate the central and northern parts of Florida as this system approaches and storm surge flooding is likely along the Gulf coast including well to the east and south of the path of the center.

Track of Hurricane Agnes in June 1972.  This system came out of the Gulf of Mexico and then pushed off the Mid-Atlantic coastline only to "back-in" before stalling out over northern Pennsylvania

Longer-term outlook (Mid-Atlantic/New England)
Once this tropical system crosses over northern Florida, it is likely to continue moving to the northeast and produce heavy rainfall in southern/eastern sections of Georgia and coastal sections of the Carolinas.  By Saturday, the system will try to head away from the Carolina coastline - but that may end up being a difficult task.  

Strong high pressure will build into the Northeast US this weekend and there is a chance that one center will slide to the east near Nova Scotia, Canada while another piece of the high pressure system hangs back over New England.  This would result in a “banana-shaped” high pressure system that could have an effect of not allowing the tropical system to “escape” into the open northern Atlantic Ocean and this positioning could ultimately pull it back towards the Northeast US coastline.  A short-wave in the upper atmosphere dropping into the picture from the Northern Plains will also become a big player in this unfolding scenario across the Northeast US.  

By no means, is the backing of a tropical system an unprecedented event in this part of the country.  Hurricane Agnes, for example, took a somewhat similar track out of the Gulf of Mexico in June 1972 (i.e., towards the northeast) , moved off the Mid-Atlantic coastline, and then backed into northern Pennsylvania before stalling out and generating historic flooding in much of the state. Of course, Hurricane Sandy also ended up taking a “left-turn” from off the Mid-Atlantic coastline into New Jersey back in October 2012.  

One concern regarding a potential tropical system sitting off the Mid-Atlantic or Northeast coastlines this weekend is that – similar to the Gulf of Mexico – waters are quite warm and actually well above normal for this time of year (i.e., favorable for maintaining the strength of a tropical cyclone).

12Z GFS forecast map for 2AM Sunday morning; courtesy tropicaltidbits.com

Computer model forecasts
The latest 12Z NAM and 12Z GFS computer forecast models actually predict the tropical system will hang along the coastline - or even a bit inland- all the way up into the Mid-Atlantic region and this track would put a real hurting on the weather in the middle of the Labor Day weekend (late Saturday into Sunday).  The 12Z Canadian model agrees with NOAA's NAM and GFS models in riding the tropical system right up the I-95 corridor this weekend.  The 12Z Euro has shifted west as well in its latest model run - mimicking the GFS model solution somewhat - and now has a strong storm just sitting off the NJ coastline come Sunday morning.  In an ominous fashion, the 12Z Euro then takes this strong system and loops it in inland across southern NJ later Sunday.

12Z Euro forecast map for Sunday morning; courtesy tropical tidbits.com

12Z Euro forecast map for Sunday afternoon; courtesy WSI

All eyes in the Mid-Atlantic and Northeast US should closely monitor this system over the next few days.

Meteorologist Paul Dorian
Vencore, Inc.

Extended video discussion: