Subtropical Storm Beryl: May 25, Update A

For fans of Douglas Adams… Happy Towel Day! (http://towelday.org/) (although by the time I finish writing this, it will be the day after).

Today I (more-or-less) agree with the NHC on their assessment and naming of Subtropical Storm Beryl! J (or that could be a couple of glasses of wine talking I suppose… it is a Friday evening after all ;-)).

Officially Beryl is currently at 32.5N, 74.8W, moving northwards at about 9mph (I’m not sure I agree with this location or direction – see later). Her central pressure is estimated to be 1001mb, with winds of 45mph (Tropical Storm range: 39-73mph). The circulation in the lower half of the troposphere has improved quite a lot since yesterday and the wind shear is dying down. There is also some circulation in the upper half of the troposphere which is a bit troublesome at the moment because it means that she has room to grow (even to a hurricane, although the official forecast has her maximum winds peaking at 50mph by Saturday evening and on Sunday, which is a weak Tropical Storm). However, she is now over cooler waters, with sea surface temperatures of 25 deg C, and no deep warm water underneath and there is still some dry air to the south and west, so there are some inhibiting factors. It looks like South Carolina is already getting some of the ‘outer bands’… i.e. a bit of cloudy (no rain) weather. As she approaches the US Coast, she will cross the Gulf Stream again and she will pick up some moisture then (time to dust off your raincoats and wellie boots!).

The NHC wrote: “FROM NOAA BUOY 41002 THIS EVENING INDICATE THAT THE BROAD LOW PRESSURE AREA OFF OF THE SOUTHEASTERN UNITED STATES COAST HAS COALESCED INTO A TIGHT...WELL-DEFINED CIRCULATION.  AROUND 2200 UTC...THE BUOY REPORTED A MINIMUM PRESSURE OF 1004 MB ALONG WITH PEAK 1-MINUTE WINDS OF 37 KNOTS...SUGGESTING A MINIMUM PRESSURE AROUND 1001 MB.” Being a sciency sort of geek, I thought I’d have a look at the data myself so I went to the National Data Buoy Center website (http://www.ndbc.noaa.gov/), one of my usual source for buoy data. At around 2200UTC, the buoy (located at around 32N, 75W) does, indeed, show a drop in pressure… to 29.65 inches! I suppose it would be too user-friendly to have them displayed in the same units (mb). Why make things easy, huh? (mutter mutter, mumble, grumble…) I did the conversion and it is 1004mb. However, the winds peaked at 34 knots, not 37 knots… therefore I think the official windspeed is a teensy-weensy bit of an over-estimate:

I know this seems like a really small amount, but the difference is that 34 knots is 39.1 mph, and 37 knots is 42.5 mph… and to name a Tropical (or Subtropical) Storm you need wind speeds of 39mph or more, but 39.1mph is too close to the border and could be within the margin of error of the instrument, whereas 42.5 mph is a solid ‘above 39’ sort of number (given it was towel day, it’s too bad they didn’t pick something that converted exactly to 42.0! ;-)). However, despite this little umm…’discrepancy’, I still agree with naming Beryl because this is just one location, and looking at the circulation, even now she looks stronger than a 45mph system.

The forecast track takes her in a west-southwest direction. Although unusual, this is possible. I think she has already started on a westward trajectory actually, and I would place her at around 32.4N, 75.4W.  She may slow down a bit tomorrow, because there is high pressure all around her (if you have forgotten the importance of this, not to worry, I’ll explain this later – maybe tomorrow, after I’ve had a nap).  The official center of cone forecast track takes her into Jacksonville on Sunday evening, but as you can see here, the ‘cone’ of uncertainty is not quite a cone:

I think it is quite possible that landfall will be north of that, in Georgia or South Carolina. The reason why it is so ‘circular’ is because of the surrounding pressure fields (high) which makes it a little trickier to forecast.

The things to watch for tomorrow are how far west she goes before (if) she slows, and where she is relative to the Gulf Stream and to land and the circulation in the upper troposphere (I’ll explain that over the weekend too). That will at least give us an indication of her intensity. She could get interesting.

Night night for now!

J.

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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.

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