Sunday, September 18, 2016

What Will Paine Bring To Us?

Tropical Storm Paine has developed southwest of Baja - above IR image is from 13 UTC this morning. The cloud shield related to Paine extends far to the northeast of the system across the lower GoC. The current NHC track forecast, below, indicates that Paine will remain a TS and curve slowly northward. The NHC forecasts the storm to dissipate before it reaches 30 degrees north.

I've taken a quick look at the 00 UTC forecast from Atmo for the WRF-GFS model on the 5.4 km grid. Above is forecast of 850 mb winds and dewpoint temperature valid at 8:00 pm MST on Wednesday the 21st. The circulation with Paine is weak, but high dewpoints have pushed northward as far as Las Vegas. The overall situation is complicated by the slow moving, cold 500 mb low that is currently west of northern Baja. The WRF forecast below is for 500 mb valid at noon on the 19th (tomorrow). Warm-core Paine is just coming into the grid at bottom of panel. The forecast indicates that the midlevel circulation of Paine will be absorbed by the northern low as Paine weakens. Eventually a remnant short wave moves into the Southwest before dissipating.

Thus, the situation is complex and the main thing that seems certain is that there will be a nice intrusion of mT air back into the Southwest. The outcomes regarding precipitation are much more uncertain. The WRF-GFS forecast of rainfall through midnight on the 22nd (bottom) indicates the main swath of heavier precipitation to extend from southern California across northwestern Arizona. The model does forecast some thunderstorms for southeast Arizona, mostly for the Sky Islands. 

The next several days will be interesting as all this unfolds.


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