Wednesday, September 28, 2011

Tropical Depression Ophelia and Tropical Storm Philippe: September 27, Update A

<Warning: tinged with a slight hint of sarcasm> For the last couple of days I’ve been calling Ophelia a Tropical Depression when really, officially, she wasn’t even that. I suppose I must have been hallucinating about the circulation and convection that she has had over the past 24 hours! However earlier this evening, after a plane went in to investigate, the NHC decided she was good enough to be reclassified as a weak Tropical Depression. Here are a couple of satellite images (visible and IR) of the Atlantic Basin, before she was ‘upgraded’ to a Tropical Depression:

You can see her just east of the Caribbean, and you can see the much stronger Tropical Storm Philippe in the eastern Atlantic… obviously she was much weaker than Philippe. <end of slight hint of sarcasm. Maybe.>

Tropical Depression Ophelia
In keeping with tradition, I expect they will turn her into a Tropical Storm when she’s over one of the islands. ;-) Although it looked like some of the islands have had a dollop of rain with a side of windy weather already (IR satellite image):

Officially she is now at 18.4N, 59.5W, moving NW at a very slow 3mph. Winds are 35mph and central pressure is 1009mb. I think they might have missed the boat on this one. I think she was a Tropical Storm, but in the last few hours wind shear has increased and the vorticity (circulation) has weakened, so it looks like she might be tiring herself out a bit. The latest satellite images show a much weaker storm than earlier today. I can’t quite tell where the center is, although it looks a little south and east of that official location.  It is also a bit tricky seeing which direction she’s heading in because she is still surrounded by high pressure. A slow NW or WNW movement is not beyond the realms of possibility. There are two factors that will work in weakening her… in addition to wind shear increasing, I’m sure the water temperature under her is cooler by now because she’s been stuck in that vicinity for about 2.5-3 days now (thank goodness she didn’t get stuck over land!). The islands might just have a lucky break if says ‘farewell’ before she can move.

Tropical Storm Philippe
Philippe is officially at 16.1N, 37W, heading WNW at 10mph. Winds are 40mph, so he’s barely a Tropical Storm (range: 39-73mph), and central pressure is 1006mb.

I am pretty sure the NHC did not have this little guy at the correct location or correct heading over the last 24 hours. At the 11pm advisory yesterday he was at 15.9N, 34.8W, heading NW at 8mph. At 5am this morning he was at 16.1N, 35.1W, heading NW at 7mph. At 11am today, he was at 15.8N, 35.3W heading NW at 5mph. At 5pm today he was at 16N, 36W heading WNW at 7mph, and now he’s at 16.1N, 37W heading WNW at 10mph. So somehow he’s consistently had a northward component to his motion, but went from 16.1N to 15.8N… hmm. Also, looking at the forecast track from a day or two ago, he is definitely farther south and west than they expected (they also had forecasted that he would be a hurricane by Monday afternoon, so that part didn’t go as they expected either). At least now they have started to move his forecast track a little more westward than directly NW! And I would agree with his direction and speed of travel.

I also agree that he is a very weak Tropical Storm. Wind shear has resulted in the convection being mostly on the northeast side of the center of circulation. But once that shear kicked in (this morning), it became much easier to see his center of circulation (visible satellite image):

Although his convection is weak, I have to say his circulation is rather strong throughout the lower half of the troposphere. If he manages to get away from this wind shear and convection picks up, he could intensify into a rather good looking little storm – but that doesn’t look likely in the next day at least, if at all.

We’ll see what our little friends do tomorrow. I think they are both interesting (i.e. a little tricky to predict beyond a day or so) for the same two reasons for now – they are surrounded (more or less) by high pressure, and they are experiencing fairly strong wind shear.

Night night!

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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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