Rather than speculating, let's do the Meteorology:
At 8:00pm, Barbados was reporting a sea-level pressure of 1010.7mbs
At 8:05pm, NHC reported a TD depth of 1008mbs, at about precisely 60 nautical miles due south of Barbados at that time.
Since NHC does not include decimal values in their depth assessments, I will go ahead and round the 1010.7mb to 1011mb for consistent units.
Ed wants to give 15mph-worth of the 32mph, back to background trade wind phenomenon, which actually is an assumption because even though trades consistently blow, they do not do so at the same velocity relative to pressure patterns. In reality, we don't know what the trade forcing into the system was as of 8pm, but for sake of discussion, we'll just assume it was 15mph-worth. That means that 17mph-worth of velocity is hypothetically storm generated.
Now, the pressure differential between Barbados and TD6 as of 8pm was ~ 4mbs. There is a general rule that works to a very close approximation: 1mb nearly = 1kt. 4mbs thus equates to 4kts.
So, immediately there is a discrepancy here. If 4mb = 4kts, 4kts certaindly does NOT atone for 17mph, considering that 1mile is 0.864 knots. That means the 4.62mph...or essentially 5mph, sticks us with an unexplained 12mph using this method. Something is adding into this to cause the +12mph
One possible explanation for this disparity is that the trade wind forcing at this time is actually stronger than usual, and thus, Ed has a very strong point: The correction may go the other way and we may yet still have a depression. In other words, even though climate argues for 15mph of trades, we may in fact have (15mph-trade) + (12mph-trade-anonamaly) to consider.
The other possible explanation is that they are wrong about the 1008mb of pressure. They do not directly specify in the 8:05 discussion whether that is based on the last RECON trip or not.
Either way, the available evidence does tend to support Ed's point of view on this.
The other thing to remember is to look at ALL the data, not just these pretty colored sat videos. Seeing as this is about to cross the axis of the Islands, we should know in a hurry if one of these islands happens through an inflow jet that is 40mph or not.
John
Edited by typhoon_tip (Sat Sep 01 2007 02:49 AM)
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