dem05
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Posts: 368
Loc: Port Charlotte, FL
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Re: GFDL
Thu Aug 16 2007 02:44 PM
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I think there is little question on the importance of the Gulfstream IV upper level wind sampling that will be occurring. This information is going to paint a much better picture of what is going on and should help the future model runs out quite a bit. I think the importance of this upper air mission is adequately stated by the NHC, as they have made reference to this flight in the last 3 or 4 Hurricane Dean Advisory Discussions.
Lots of talk on the evolution of the high, the Cut off low, and other features that may affect Dean. In looking at the current models, I also share concern that the models may be making the overall atmosheric dynamics too straight forward. With respect to the GFDL, this is one the most reliable hurricane forecasting models and this model always gets very heavy weigh in on forcast tracks. With that said, I think last nights GFDL was weakening Dean during the forecast period, as it was seeing a system that would head into the Cutoff low and experience shear. As for todays model runs so far, the GFDL seems to have recognized that Dean is more formidable than the weaker tropical counterparts. As a result, the GFDL now sees an interaction with the cutoff low that moves it NWward, versus lasts nights representation that moved Dean under the cutoff and into a sheared environment.
Now, back to the Upper Low, the high pressure ridge and possible steering consequences. I'm gonna dive into the Water Vapor here, and I'd only like to base my interpertations on how the steering flow may change over the next 24 hours. Tomorrow, I will likely post a similar post looking at the next 24 hour period.
The View across the Atlantic: http://www.ssd.noaa.gov/goes/east/tatl/loop-wv.html
- The cutoff low does not appear to be weakening, it is moving to the west very slowly,but probably not as fast as one would expect based on the models...This could be an implication, since Dean is making some headway on the cutoff low.
- There is indeed a trough affiliated with the cutoff low, and the trough does extend pretty far into the Carribean.
- True, the Ridge of High Pressure is moving westward and placing some pressire on the southern extent of the Cut-off low/trough. However, I am somewhat concerned about the cutoff low that is also moving westward and centered around around 30N, 46W. The reason for concern is that the interaction of the Bahama'slow and this low may change the orientation of the ridge...instead of the ridge being oriented E-W as forcasts indicate, the ridge may become oriented in a N-S direction. This may hinder the westward progress of the Bahama's low in the coming day or so. It may also hinder the continued westward advancement of the ridge that the models want to depict.
- Finally, I notice a weak (albiet Small) upper level low trying to form ahead of Dean along the South American Coast. (Around 10N and 62.5W). This would have little impact on Dean from a shearing prospective...But as this kink in the upper level winds continues to prog westward, it will be curious to see if this links up with the Bahama's Cutoff Low and increases the southerly flow.
The View across the CONUS: http://www.ssd.noaa.gov/goes/east/nwatl/loop-wv.html
- AT this point, the jet stream looks fairly zonal...no real troughs or ridges...so nothing to really move the high over the Missippi Valley/Georgia area too much (considering the ULL over the Bahama's). However, in looking downstream, the ridge over the MissValley/GA also extends into the Northern Gulf and western Gulf States (On the western side of the ULL. So even though the Atlantic Ridge is pushing on the Baham's Low from the east, the High over the Southeast is pushing on the Cutoff low from the west. Talk about mother nature's power play...
In sum, I do not expect the upper level low over the Bahama's to make as much westward progess as was expected during the next 24 hours and the bottom line is this...Dean is making faster forward progress to the west than the Baham's low. Dean and it's anticipated 200MB ridge will push back on the ULL when they get a little closer to one another, but if the Upper Low does not fade away in the next 72 hours, I would not be surprised to see Dean on a more NWerly or Nerly route in days 4-5. That Gulfstream Jet Data is gonna be very important to the upcoming forecasts. I will not be surprised to see the models shift to a little more northerly route over time...much like the GFDL is starting to do now. Mean time...In another 24 hours...it will be interesting to look again and post on what is expected with the upper level dynamics through Saturday...
Edited by dem05 (Thu Aug 16 2007 03:02 PM)
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