Good morning all. Delta is so very interesting. I have been watching storms all season now, but have not seen anything like this. It looks so strange on the visual sat images, almost like it is forming in reverse of what I have gotten used to seeing with TC, starting at the outside and working in. The wind field has consolidated as it has strengthened, but it seems the core will will be the last part to develop. I stared at the visual loop for a long time this morning (luckily it's all the same to the furball, who is very non-judgemental anyay, but fortunate really that no one was watching, or they'd wonder if the closest I could get to a brainstorm would be a light drizzle). It may seem odd, but visual imprinting of all these images makes a great reference tool for recognizing things down the road.
Looks like Stewart is holding down the fort at NHC TPC for the holiday. I so enjoy reading his discussions. He has a knack for clarifying things, using terminology that most everybody can understand. He explained the outflow, something I was wondering about yesterday, wondering where the anticyclonic flow could come from since Delta is moving within a larger low:
DELTA IS CURRENTLY LOCATED BENEATH AN UPPER-LEVEL SHEAR AXIS ALONG 38-39N LATITUDE. THIS HAS ALLOWED FOR THE VERTICAL SHEAR TO DECREASE AND FOR ANTICYCLONIC OUTFLOW TO DEVELOP. THE 300 MB WINDS ARE DEPICTED BY ALL THE GLOBAL MODELS AS BEING AT LEAST 20 KT LESS THAN THEY ARE 200 MB... SO THE SHIPS MODEL VERTICAL SHEAR ANALYSIS OF 42 KT APPEARS TO BE TOO STRONG. THE MODELS MAINTAIN RELATIVELY WEAK 300 MB WINDS OVER DELTA FOR THE NEXT 24-36 HOURS...
And he again emphasized the importance of organized convection around the center, and the resulting difference between a normal eye and the center around which the clouds are swirling:
AND THE ONLY REASON THE INTENSITY WAS HELD DOWN WAS DUE TO THE LACK OF ANY CONVECTION IMMEDIATELY SURROUNDING AROUND THE EYE FEATURE.
The track forecast is really excellent (remember Beta...and when to follow the models):
THE INITIAL MOTION ESTIMATE 090/02 KT. WATER VAPOR IMAGERY AND RECENT SATELLITE POSITION ESTIMATES SUGGEST THAT DELTA MAY HAVE BOTTOMED OUT AT THE BASE OF THE LARGE TROUGH/CYCLONIC GYRE IN WHICH THE CYCLONE IS EMBEDDED. THE MAJORITY OF THE NHC MODEL GUIDANCE CONTINUES TO TAKE DELTA SLOWLY SOUTHWEST AND THEN WESTWARD BEFORE TURNING IT BACK TO THE NORTH... DESPITE THE BROAD COUNTER CLOCKWISE MOTION THE CYCLONE HAS MAINTAINED FOR THE PAST 48 HOURS. WHILE IT IS POSSIBLE THAT DELTA COULD MAKE SOME SMALL LOOPS OR WOBBLES TO THE SOUTH OR SOUTHWEST... THE OFFICIAL FORECAST CALLS FOR LITTLE MOTION FOR THE NEXT 24 HOURS. THE CYCLONE IS EXPECTED TO TURN BACK TO THE NORTH BY 36 HOURS. THE OFFICIAL TRACK IS A LITTLE TO THE EAST OF THE PREVIOUS ADVISORY FOR THE FIRST 36 HOURS TO ACCOUNT FOR THE MORE EASTWARD INITIAL POSITION... BUT THEN COMES BACK ON TRACK BY 72-120 HOURS. A NORTHWESTWARD TURN BY 120H IS EXPECTED DUE TO SOME BINARY INTERACTION WITH AN EXTRATROPICAL LOW PRESSURE SYSTEM THAT IS FORECAST TO DEVELOP TO THE WEST OF DELTA.
The best part of tracking these storms for me is watching the visual images, but the second best part has to be reading the NHC TPC discussions. You often hear the phrase that this or that scientific pursuit is an art (such as, forecasting is an art), and as a large part of myself is an artist, I'd have to agree that there is a point where all the logic and knowledge meet with that other intuitive process, and these people on staff at NHC TPC have both the knowledge and intuition, in spades. The discussions not only provide color in the B&W numerical world of meteorology, but manage, within the many guidelines and limitations inherent with the required wording and the product (not to mention the politics involved), to reflect each individual forecaster's personality as to how they approach the forecasting process.
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