10:35 AM (Friday) | ***Hurricane Dorian continues on a track towards the Bahamas and Florida…could reach category 4 status...a slow-down is likely…potential turn up the east coast next week***

The latest satellite image reveals the beginning of an “eye” formation as Hurricane Dorian continues to intensify. Courtesy NOAA

Overview

A serious weather situation continues to unfold as Hurricane Dorian intensifies and continues on a path towards the Bahamas and Florida with possible landfall later Monday into Tuesday.  Hurricane Dorian has reached category 2 status as of early Friday morning and could reach “major” hurricane status (i.e., category 3) later in the day.  High pressure ridging in the upper part of the atmosphere is a key player in the intensification and movement of Hurricane Dorian and it should result in additional strengthening over the next couple of days – perhaps to category 4 status. 

As Hurricane Dorian nears the northwestern Bahamas later this weekend, the upper-level ridge will tend to weaken and this is likely to result in a slowing down of the system. The weakening ridge may also allow for a turn to the northwest as Hurricane Dorian approaches Florida and then a turn to the north and northeast once near or just over land.  This could very well result in a slow trek up along the eastern seaboard later next week; in other words, we may still be talking about Hurricane Dorian a week from now. 

00Z Euro forecast maps at 500 mb for Saturday evening (left) and Monday evening (right) with a weakening of the high pressure ridge (shown in orange) to the north. Courtesy NOAA, tropicaltidbits.com

Discussion

Hurricane Dorian has increased in intensity in recent hours with maximum sustained winds at 110 mph, movement to the NW at 10 mph, and is on the doorstep of attaining “major” hurricane status (i.e., category 3+).  A key player in the strength and track of Hurricane Dorian is an upper-level ridge that has developed over the western Atlantic Ocean.  This upper-level ridge is already influencing Hurricane Dorian and has generated more favorable atmospheric conditions for intensification.  When an upper-level ridge develops over and just to the north of a tropical system, it tends to result in lower wind shear in the general vicinity which is favorable for intensification.  In addition, an upper-level ridge leads to divergence aloft and convergence near the surface which increases the overall upward motion in the general area – also favorable for intensification.  The wind flow around the southern part of the upper-level ridge is primarily in a westerly direction and that is going to result in a slight, but important shift in the path of Hurricane Dorian from northwest-to-west – and right to the Bahamas and towards the east coast of Florida. 

As upper-level ridging intensifies, wind shear generally decreases in the general vicinity and this tendency of decreasing wind shear just out ahead of Hurricane Dorian will aid in strengthening in coming hours; courtesy CIMSS/University of Wisconsin, NOAA

Often times, there is significant intensification of a tropical system at the time of this type of “bend” in the storm track from northwest-to-west as was the case, for example, with Hurricane Andrew in 1992.  The “bend” is a signal that high pressure ridging is indeed intensifying aloft which, in turn, favors intensification for reasons described earlier.  In addition to the favorable factors for intensification associated with the high pressure ridging aloft, Hurricane Dorian is moving over very warm waters of the southwestern Atlantic Ocean which also favors strengthening.

Many computer forecast models have predicted storm tracks for Hurricane Dorian which would result in landfall along the east coast of Florida and then a right turn to the north/northeast; courtesy sfwmd, NOAA

By the latter part of the weekend, signs point to a weakening of this all-important upper-level ridge to the north and this could result in a last minute turn to the northwest or north as Hurricane Dorian approaches the east coast of Florida.  This likely weakening of the upper-level ridge should also result in a slowing down of the storm as it nears the Bahamas and Florida Peninsula. Eventually, a turn to the north and northeast is likely once Hurricane Dorian is near or just over land and this could very well result in a slow trek up along the eastern seaboard later next week which means we might still be talking about this same system a week from now. 

This is the forecast map of NOAA’s main hurricane model called the HWRF that verifies on Monday evening at 8pm; courtesy NOAA, tropicaltidbits.com

A historical perspective

If Hurricane Dorian does make landfall in Florida, it will be the fourth year in a row with a landfall in the state of any intensity magnitude (Hermine 2016, category 1; Irma 2017, category 4; Michael 2018, category 5). The most consecutive years in Florida with landfalling hurricanes is 7 which took place between 1944 and 1950.  If Hurricane Dorian reaches Florida as a category 4 hurricane, it would be the third year in a row for that kind of “major” hurricane status.  The last time that happened in Florida occurred between 1947 and 1950 when there were 4 years in a row with a landfalling category 4 hurricane. 

An even more active stretch of hurricanes for the state of Florida took place in the late 1940’s. Courtesy Philip Klotzbach (Colorado State University, right plot), Weather Bell Analytics (left plot)

Bottom Line

All residents in Florida should continue preparations for a possible “major” hurricane hit in the time period of later Monday into Tuesday.  In addition, all residents up along the Atlantic seaboard should closely monitor the situation as Hurricane Dorian could take a slow ride up along the east coast later next week. For more information on preparing for a hurricane visit this NOAA web site.

A historical look at tropical systems in the same general vicinity of Hurricane Dorian suggests it is usually quite difficult to make it all the way west to the Florida Peninsula. More often than not, a tropical system in the same general location of Hurricane Dorian during the past couple of days turned northwest or north just as it approached the east coast of Florida. Courtesy NOAA, ESRI

One final note of caution, any time a system slows down as Hurricane Dorian is sure to do, it opens the door for unforeseen scenarios so stay closely monitored to the situation over the next few days. A scenario that is certainly still on the table based on historical comparisons with other storms in a similar location is that the center of Hurricane Dorian never quite makes it as far west as Florida which raises the possibility of landfall in Georgia or the Carolinas.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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