Saturday, August 22, 2015

Hurricane Danny: August 22, Update A

Hey look, Danny has weakened and is now officially a cat 1 storm with winds of 90mph (central pressure estimated 985mb)! (Cat 1 range: 74-95mph). Hurray! :-) 

Actually, looking at his visible and infrared satellite imagery, I would say he's weaker than that because he's not had an eye for a long time (as seen in the visible image)...

and the convection is looking quite ragged and not as concentrated in the infrared...

As I explained yesterday, this is in response to both the wind shear and the SAL. He is still moving through the region of high wind shear and dry, dusty air. You can see the impact of the wind shear in the satellite images with the clouds streaming off to the northeast. 

Also, although his circulation is strong in the lower half of the troposphere, there is a definite weakening in the upper troposphere, which means he is losing that strong structure that makes him a hurricane. I would say he is a fairly weak cat 1 storm at this time, with winds around 75-80mph. 

Another satellite image to look at is the water vapour:

You can see the dry air he is moving through... but this also shows us the approximate area of high pressure that he's been bumping into - that paler brown region to his north and west, stretching across the northern Caribbean. The NHC think that the high pressure will rebuild to his north, which is why they are maintaining a track to the west and over the northeastern Caribbean islands (including the VIs) on Monday/Tuesday.

This is quite possible, but they have been consistently tracking him a smidgen (technical term ;-)) to the south of the actual storm position at two days out, so although he could pass directly over, he may also just skim to the north. The cone of uncertainty is the thing. In either case, he will be much weaker by the time he gets there. 

More tomorrow... with hopefully a 'Tropical Storm' Danny on the books!

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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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