GFS random lows in the caribbean/BOC possible reason... (?)

[Anonymous]

I have noticed the GFS seems to be forecasting a lot of 'Ghost storms' in the caribbean. Reminds me of the old MRF before the AVN and MRF became the GFS. But GFS done pretty good last year and didnt create and aweful lot of storms that didnt materialize like it has this year in the first 3 weeks of cane season... Off to a bad start I think. Maybe, it is because the GFS sees the lower than normal pressures in the caribbean and tends to pick up on a thunderstorm complex that may form---perhaps overland and move offshore due to afternoon convection and form a low/convective feedback. Or maybe it is just having a hard time with the lower than normal pressures that have persisted in the caribbean so far and forming storms. It will eventually be right again as it was with Arlene though as I said last week, pressure is lower over such a large area that pressure would have to drop good bit lower than your average TD to get a TD and be lower than already lower pressures. And it think that is reasonably hard to do and may be as rare as the High pressure hurricane danny of 2003 with a lowest pressure @ 1005 MB because it formed into a 1015 MB TD in the Bermuda High LOL. http://weather.unisys.com/hurricane/atl ... /track.dat Comments welcome

BTW, quick question, what would have happenned to Danny if it had moved outta the high pressure dome as a hurricane? Say it headed west toward the US, would the pressure have dropped or would the storm have weakenned?

[weatherwindow]

very reasoned argument....makes intuitive sense. low environment pressures are certainly a plus for development, imagined or otherwise. as far as danny was concerned....i believe he would weaken. two reasons: 1)he is by definition moving from under a deep layered high(excellent outflow) to an area of lower pressures aloft, hence increased shear. 2) the pressure differential would ,by neccesity, be reduced. the central pressure is semi-fixed and based on internal dynamics and ventilation. while the environmental pressures are reduced. a friend of mine was fond of saying that the rule of thumb is that, all things being equal, a 10mb pressure differential will support a whole gale in the right front quadrant.....IMHO, danny will weaken, how much will be determined by the resultant change in the press diff compounded by increased shear and reduced ventilation......................rich

[wxman57]

As for Danny, I don't believe that Danny had so high a central pressure. There was no recon and I don't believe that there were any surface reports in the area. I'm not sure what the NHC used as a basis for Danny's pressure? Anyone?

[Derek Ortt]

which Danny?

1997 prior to recon they used oil rigs

2003, they used the ambient pressures from the limited obs that they had, which did indicate much higher than normal pressures in the area, creating the very high pressure, but low enough to support a hurricane