Hurricane Dorian: August 29, Update A

No point flaffing around today...  

Hurricane Dorian is still a cat 1 storm with a very small eye that is appearing intermittently (according to aircraft data - not so easy to see in the satellite imagery). Along with the circulation in all levels of the troposphere, this means his wind speed was somewhere around 90mph which means he was a little stronger as a cat 1 storm (cat 1 range: 74-95mph), but the eye hasn't been seen for a few hours so the latest official update has his winds at 85mph, central pressure 986mb. I'd say he is a little stronger, but agree that he is still a cat 1 storm. 

He will steadily get stronger because of the reasons I gave yesterday (low wind shear, sufficiently warm waters, moist air, and no land). I see that the NHC have increased his intensity forecast since yesterday, saying that he will be a major storm (a cat 3 or higher) in the next 24 hours. There are a couple of reasons that this may happen. First, he will be passing over a patch of slightly warmer water (29 deg) north of the Turks and Caicos, however the water does get shallower in his path so that will not be too much of an effect. Second, there is a low pressure front with a lot of circulation in the upper troposphere and I've seen storms intensify when they go through one of these. So, there is a possibility that he will be a cat 3 tomorrow, but I think most likely he'll be a strong cat 2/weak cat 3.

He is currently at 22.5N, 67.7W, heading NW at 13mph. How strong he gets before landfall in Florida depends on his track as he gets closer to Great Abaco and Grand Bahama. The track has been shifting slowly south, bringing him a little closer to that portion of the Bahamas (sorry Bahamians!). Those are the only pieces of 'land' that would inhibit his growth - but not by much. The major factor in intensity change between him and Florida is really the Florida Current/Gulf Stream system, which he has to cross.

<Science Alert!> The Florida Current: This is part of an ocean current system that flows from the Caribbean into the Gulf of Mexico through the Yucatan Strait, and then out of the Gulf of Mexico through the Straits of Florida, and up the east coast of the US. It leaves the US coast around North Carolina and flows across the north Atlantic to the UK. When it is in the Gulf of Mexico, it is known as the Loop Current. As it exits and flows past Florida, it becomes the Florida Current (because we like things to be named properly), and then beyond Florida it is known as the Gulf Stream. The Loop Current can extend quite far into the Gulf some years, and not so far in other years. So why is this current system important for tropical storms? This system is well known because it has the deepest warm waters (and is very fast flowing). The deep warm waters (the upper 125m can be warmer than 26 deg C) mean that tropical storms that pass over any part of this system have a jolly good (British understatement) chance of becoming stronger. <End Science Alert!>

(ooh, look at me, sneaking in a bit'o'science! It's just like the old days... ;-)).

If he is a cat 3 as he approaches the Florida Current, there is a good possibility (everything else being equal) that he will be a cat 4 at landfall as he crosses this current (but if he's a cat 2, then cat 3 is a possibility). Don't take this as definite yet - tomorrow we will know more because this all depends whether he gets to that cat 3 stage tomorrow or not.

As for his track... alas, there is HUGE uncertainty in the models which is why the entire east coast of Florida (and a tinsy bit of Georgia) is on alert (I'll rant about this at some future point - no time today!):

Remember not to focus on the center of the cone of uncertainty - the entire area is where the storm could go - at four days, that covers a range that is 155 miles long, and at 5 days out, that covers 205 miles! 

For those in west Florida, generally he will downgrade by two categories as he crosses the peninsula (unless he goes over Lake Okeechobee or the Everglades). 

As you prepare, in addition to my usual hurricane supply check list (which obviously features ice cream and wine in sufficient quantities ;-)), here's the link (thanks to Yoav R. for sharing) from the State of Florida for hurricane preparedness. 

Stay safe out there! Get ready!

J.

Twitter: jyovianstorm

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DISCLAIMER:
These remarks are just what I think/see regarding tropical storms. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast. This is not an official forecast.
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