Monday, September 13, 2010

Hurricane Igor, Tropical Storm Julia, and the Caribbean Blob: September 13, Update A

This week is the statistical peak of the hurricane season... it's all downhill from here and then it'll be hibernation time. Yay! ;-)
Hurricane Igor:
I must say, Igor is a very handsome looking storm! His mum (Mother Nature) must be proud. He's been holding pretty steady all day today as a very strong category 4 storm with winds of 150mph (cat 4 range: 131-155mph) and a central pressure of 933mb. He has also continued to head west and has slowed down a bit to 10mph. The center of the storm is at 17.7N, 50.5W but hurricane force winds (greater than 73mph) extend out 50 miles from the center and tropical force winds (greater than 39 mph) can be found upto 195 miles from the center.
Intensity: "The Force is Strong with this one" (Star Wars). ;-) It looks like his vorticity has improved throughout the troposphere so I wouldn't be overly surprised if he's actually a cat 5 storm (cat 5 winds >155mph), but if the NHC want to keep his winds officially at 150mph that's fine. At those velocities, what's 5mph between friends, hey? Wind shear is low and looks like it will remain low for the next day at least, so that won't hinder him. Convection is, of course, strong. Sea surface temperatures are a warm 29 deg C with waters warmer than 26.5 deg C in the upper 75m (and he's heading towards areas where the warm water is in the upper 100m). There is some dry air ahead of him and to the north but I don't think it's enough to do him much harm anytime soon. I think I'd have to agree with the NHC at the moment and say he's going to remain a major hurricane for the next day or two at least.
Track: Hmmm. I'm not overly pleased that he's still moving westward. The forecast track has been slowly inching to the west, but they still say he's going to turn to WNW and then NW tonight. He is following the southern edge of a high pressure (science snippet: in the northern hemisphere things move clockwise around a high pressure system). The models (with a couple of exceptions) are forecasting that the high pressure will erode and be replaced by a low pressure, which will allow him to move NW (clockwise) around what's left of the high pressure. This is forecast to occur any second now and I think he might actually be doing that. Either that or he's having a wobble. We won't know for a few hours (by which time I'll be asleep) so tomorrow morning let's see if he's crossed 18N. Of course, the farther west he travels, the closer he gets to the northern Leeward Islands of the Caribbean. And if he turn WNW and then NW, he's heading towards the Bermuda region. Sigh.
Tropical Storm Julia:
My Atlantic Blob turned into a Julia. ;-) She's currently a weak-to-mid-sized Tropical Storm with winds of 50mph (range: 39-73mph) and an estimated central pressure of 1000mb. She's too disorganized for me to see her center so I'll go with the official NHC location at 15.3N, 27.5W. She is moving WNW at 14mph - following in her big brother's footsteps. Water temperatures are 27-28 deg C, so warm enough to keep her going (tropical storms need sea surface temperatures warmer than 26.5 deg C). Her vorticity is really quite strong for this size Tropical Storm. I think she might be a bit stronger than the official forecast (but I don't think she's a hurricane). 
Caribbean Blob:
I know I wasn't going to mention this blob until it got enough signatures to petition to become an official Tropical Depression, but I thought it worth mentioning that the vorticity (circulation) has improved during the day and is stronger in the lower half of the troposphere now. The convection still remains a mess, but Jamaica and parts of Cuba got a good shower or 10 today. It's moving WNW at 20mph. If it can pull itself together (circulation and convection), there's a chance it will develop further.
That's all for today.
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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 was there and was going to "run away, run away" (Monty Python), I'll let you know.

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