Wednesday, September 05, 2007

Forecast Remains Difficult

See yesterday's message about tough forecasts!

Today we have moisture and hopefully CAPE will remain through the day -we are getting some mid-level warming now. Upper-level winds are difluent between the hurricane and the system to NW. Winds are very light in lowest half of troposphere - again. Low-level winds become southwesterly during the day and there is more IPW to the west. So, there should be storms around this afternoon with the potential for heavy rains.

Tomorrow is much tougher and it's possible that it will be an all or nothing situation here in the Tucson area. Who remembers Nora?

NAM forecasts a decent rainfall event, but keeps the really heavy rain with the core of what was Henriette. It is of note that there were soundings this morning at La Paz and Guaymas for the first time in ages, so the model actually had some observations in its initialization.

Negatives tomorrow are that NAM forecasts winds to become strong downslope below 500 mb into the local area. This is coupled with what appears to be fairly strong confluence aloft. The GFS members forecastsignificant rain event also but, of course, local terrain really isn't in that model.

If the remains of Henriette move northward to the west of the NHC and NAM tracks, get out the sandbags!

So, I conclude that, with so many uncertainties in the next 24 hours, the only thing to do is to watch the observations closely and see what actually transpires during the afternoon and night.

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