Rob_M
(Weather Hobbyist)
Thu Jul 22 2004 06:11 PM
Re: IWIC afternoon discussion

lol Phil...yeah I figured it was only a matter of time before our scoring streak ended. But the track is, or would have been, just as expected...westward rather than being picked up by the trough as some speculated could happen. Now this still doesn't change the prospects for the season (read below). And congratulations to Rabbit. You nailed this one.

BTW here's the whole discussion since Phil posted the first paragraph.


IWIC Atlantic Tropical Weather Discussion - 22 July 2004 - 1:20 PM EDT

The tropical wave traversing the central Caribbean Sea has been devoid of any deep convection for about 18 hours. In fact, there are no more hints of a mid or low-level circulation either. Yesterday, we expected the wave to slowly intensify as it moved westward, though this is apparently not going to be the case. The explanation is quite simple, the wave had upper level support yesterday and today it does not. To put it an other way, there was an upper level low positioned just north of the system, which induced moderate shear aloft in the area. In turn, divergence increased, and the lead result of that was more lift and enhanced convection over the wave. Today, the wave has moved west of that upper level low and shear, so it has nothing else to sustain convection. Therefore, it is not surprising that we are not seeing any convective "blow-up".

The environment ahead of the wave actually still looks conducive. The favorable conditions will not mean much, however. If there was already a pre-existing mid to low-level circulation and convection as we earlier thought would be the case, then it would have a chance. Since it does not, it will not have the time to regain organization, regardless of how supporting the conditions are. And since the wave is now simply just a wave, it will be completely governed by the low-level steering flow from the subtropical ridge. This will take it on a quick westward course. It should be noted that even the wave still had a low-level circulation, a westward track would still occur, as the steering flow is easterly at both the mid and low-levels of the atmosphere. This was one aspect we correctly forsaw a couple days ago. What did not occur as expected was intensification after moving out of the upper level's grasp.

Another point that needs to be brought up is the hurricane season itself. With the failure of this to develop, we still stand at 0 named systems for the seasonal total. This is not that unusual, as on average we would have seen about 1 named storm by July 22. An active season with 14 named storms, 8 hurricanes, and 4 major hurricanes is still forecasted. All of the known parameters that influence Atlantic Basin tropical cyclone activity point towards a significantly above average peak, particularly in the Mean Development Region. These parameters include low tropical shear, northward positioned Intertropical Convergence Zone, low sea level pressure anomalies, warm sea surface temperature anomalies, westerly Quasi-Biennial Oscillation, no El Nino, and a strong thermahaline circulation.



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