Many of us are focused on our Labor Day forecast and how it impacts our plans and it’s a pleasure to report New England should remain dry for most of the holiday weekend.
A low chance of showers does exist, however, particularly in Western New England Sunday and for all of us Monday. Many are also paying close attention to Hurricane Dorian, and with good reason.
As Dorian churns north of Puerto Rico Thursday and chugs northwest, the best news has come for the Turks and Caicos, Haiti and the Dominican: all were in the potential path earlier in the week, and all will see the storm sail north, instead. That said, not everyone is breathing a sigh of relief, of course.
The ocean waters ahead of Hurricane Dorian are warm – in the 80s, and warm enough to support a Category Five Hurricane if atmospheric conditions are perfect. Perfect atmospheric conditions rarely are present around a hurricane, however, and this time around is no exception.
With that said, the combination of warm water and at least moderately favorable winds aloft are the reason the National Hurricane Center forecast predicts Dorian will strengthen to a Major Category Three Hurricane as it draws closer to the Northern Bahama Islands and Florida’s Eastern Coastline.
For this reason, residents of Florida have already begun early hurricane preparations, which at this stage of the game often includes making sure insurance documents are in place and that supplies are on-hand. Such items will be useful for boarding up windows and the like, though we’ve not yet reached the point where hunkering down is necessary.
Interestingly, for all the progress weather technology has seen over the years, there are certain facets of a hurricane that make it still inherently unpredictable. The focal point of these unpredictable angles are the heat engine within the storm and surrounding atmospheric wind, especially aloft.
As a result, the average error in a hurricane forecast four to five days out is on the order of 200 miles! Intensity forecasts also struggle with an average error four to five days out of 20 to 25 mph in sustained wind. So, when we look at a National Hurricane Center forecast and see the cone of predictability, the explanation for the size of that cone – increasing the farther out in time you go – relates entirely to the average error of hurricane forecasts.
That’s why, from our Thursday perspective on a Monday storm potential in Florida, you’re looking at a potential landfall ranging from South Florida to Georgia. Or, keep in mind, still within the cone of probability would be a solution that slows the hurricane just off the coastline.
The potential of a slowing solution off the coast is a real one, given strong jet stream disturbances moving through the Northern half of the United States late this weekend into early next week. One would think disturbances so far from the hurricane may not have much influence, but it can be quite the opposite.
Hurricane steering currents of wind are often a very delicate balance between tropical winds and northern winds, so the way they interact is key in where a hurricane tracks. In this particular instance with Dorian, a large dome of high pressure over the Atlantic is the reason the storm will track west toward Florida, but a northern disturbance aloft and surface cold front become key.
If the northern disturbance dips south, it could influence Dorian enough to slow the storm near the coast, opening the door to a northward drift. If the northern disturbance is not very strong, Dorian would continue directly west into Florida.
Either way, New England, at this point, looks unlikely to take a hit from this storm.
The northern disturbances that may influence the hurricane will be so influential this far north, that the steering flow will have very little opportunity to turn northward enough to carry the storm this far north.
That said, if Dorian does end up sitting along the coast or drifting north early next week, some swell may reach New England by midweek at our South Coast, so we’ll keep an eye on the track for the potential of some higher surf, but not a hurricane strike.