Monday, August 22, 2011

TD Harvey & TS Irene: August 21, Update C

TD Harvey:
I thought I might as well keep going, because apparently he is still going. We are all having a difficult time finding his center (e.g. from the NHC at 11pm EST: “THE CENTER OF HARVEY HAS BEEN VERY DIFFICULT TO LOCATE THIS EVENING.”) So he’s not a very well developed system, and it’s really tricky to tell if he’s even over the Bay of Campeche, even though it did look like he might have made a move in that direction. His last estimate from the NHC was at 19N, 95W, moving WNW at 12mph. I think he’s already west of there, and has made landfall in Mexico again. Winds were weakish at 35mph, central pressure estimate 1005mb. Although convection increased during the day, it should begin to decrease again soon. So this is my last entry on this system – really this time!

TS Irene:
The latest NHC advisory has her located at 17.9N, 65.5W moving WNW at 15mph. Her winds are now at 70mph, which makes her almost at hurricane strength (TS range: 39-73mph) and her central pressure is 993mb. The track has shifted northward and eastward during the day, which would reflect the fact that the center was on the northernmost edge of their cone this morning (actually looked like it was just north of that). She has officially passed the US Virgin Islands and is about 50 miles SE of San Juan, Puerto Rico now, although the entire area is getting rainy and windy sort of weather. Hurricane watches have been posted for the entire area, including the VIs. They are telling everyone not to focus on the track at 4-5 days from now because there is a huge amount of uncertainty in this. I agree and will explain below.

Intensity: She is just about leaving the Saharan Air Layer now, so her convection has improved and will continue to improve:

I would be surprised if we didn’t wake up tomorrow to our first hurricane of the season. Wind shear is not very strong compared to the storm, so that will only have a slight impact. Water temperatures are still in the 29-30 deg C range at the surface, with waters warmer than 26 deg C in the upper 100m. The only thing that will slow down her development is the land masses of Puerto Rico and Hispaniola (and possibly Cuba if she interacts with it in the future).

Track: Her track was pretty much as I thought earlier – she hit the northeastern Caribbean islands and the forecast shows her clipping the northern side of Puerto Rico and the Dominican Republic:

At least that is what the latest center of the cone is showing. Umm… however… there’s this little niggling voice in my head that is saying that now she’s managed to visit every island up there, she might actually take a more westward track tomorrow, or she might slow down and stall. The reason I say this is because there is an area of high pressure in front of her, which means that it is like going uphill for her, which she won’t like to do (because storms are lazy ;-)). If she moves W (or even WSW), the track will shift towards the south and west again. If she slows down or stalls, that’s another scenario entirely because where she slows/stalls will impact her intensity as well. I could be completely wrong, which would be fine with me because I don’t particularly like either of those scenarios compared to her current forecast track.  

Reports from the field:
I’ve heard from Tom in St. Thomas throughout the day and I posted some of his notes earlier. The latest one was at 8.08pm:
“wind in north quadrant is very strong and must be close to 60mph. lots more rain north of this storm and it is powerwashing St. Thomas, the strangest thing of all is that the electrical power here where we live has been on more than off. with the wind as high as it has been all day just can't figure that more power lines are not down. with the bulk of the weather north of us now I figure the center will move more northward as well which may spare florida. fingers crossed!”

I also heard from Debbie, whose mum (on St. Thomas) said that they were under a curfew on the island from 6pm until 6am.

Thank you for the reports from in the field! I hope everything is ok over there and you are all safe.

More tomorrow!

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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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