Sunday, August 26, 2012

Increase In Storm Activity Today

Weather interest today will be centered on TS Isaac, as it heads into the Gulf of Mexico. Forecast models forecast strengthening into a hurricane, but remain to have a large spread for Isaac's track after 36-hours. This leaves uncertainty about where the storm might actually make landfall - so, emergency managers along the Gulf Coast as far west as New Orleans will be facing a tough decision making situation today and Monday. First day of Republican Convention has been cancelled - short-term weather they accept.

Precipitable water is creeping up over southeast Arizona and decreasing over southwest portion of the state (above is CIRA blended PW product for 12z this morning, 26 August, with green shades indicating amounts from 1.00" to 1.50"). I found no reports of rainfall in eastern Pima County for past 24-hours, however there were Cbs off to east and northeast during the afternoon. This morning's Tucson sounding (skewT below from SPC) indicates that upper-levels have moistened up some. Winds aloft are light and variable - the 500 mb anticyclone is centered in northwestern New Mexico and at 250 mb it is nearly overhead. The sounding indicates, at most, a sliver of CAPE at low elevations this afternoon.

The early run of the WRF-GFS model (above is forecast of composite radar echoes at 4 pm MST this afternoon) indicates increased thundershower activity to the east of Tucson today. Some Cochise County storms make it west to near the Rincons, before dissipating. The total rainfall predicted by the WRF-GFS through midnight tonight is shown below.

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