How much rainfall many locations, such as here at the house, in Arizona have for September will depend on how things evolve between Tropical Storm Georgette and the approaching Pacific trough. Georgette (top IR image) was spinning away yesterday, and was officially named early this morning. She is forecast to move north up the GoC while weakening into a remnant.----------------------------------------------------
This morning (Tuesday, September 21st) finds southern Arizona having PW of 1 1/4 to 1 1/2 inches, with the very deep moisture lurking north of Guaymas. The morning Tucson sounding (middle graphic) indicates a bit more CAPE than yesterday but still with two flow regimes - baroclinic westerlies ahead of the Pacific trough overlie light winds in the moist lower troposphere below 500 mb. No good steering flow yet and and a warm upper-troposphere remaining hostile to deep convection. Both the midnight WRF run and this morning's NAM run forecast convection this afternoon and evening to again remain mostly on the higher terrain (see previous post). However, the models forecast deep tropposperic southerly flow to develop during the night and to persist 12-hours or so, before the Pacific trough sweeps by. It is during this period that the models forecast a very significant precipitation event for much of Arizona. Both the WRF and NAM forecast an early am rainfall burst between midnight and sunrise tomorrow (see NAM 6-hour rainfall ending at 5 am bottom graphic). The WRF nocturnal event is forecast to be centered further east by about 60 to 100 miles. It will be interesting to see how the morning Atmo WRF runs develop the precipitation event! Regardless, an interesting weather event unfolds after a long, hot, dry spell!
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