Tuesday, August 18, 2020

Hurricane Genevieve

Haze and smoke making for dirty air over Tucson area again this morning. There are two small fires burning in the Rincons which are contributing to this problem. Plot of detected CG flashes for 24-hours ending at 1:00 am MST this early morning (below) shows that thunderstorm activity yesterday stayed mostly to the north and west of southeastern Arizona. Phoenix had its second day in a row with nasty haboobs and low visibility in dust.

To our south, Hurricane Genevieve developed and intensified rapidly during the night - storm is rated as Category 4 this morning and forecast to intensify to Cat 5 later today. Morning forecast track (above from NHC) takes the storm northwestward, just off coast of southern Baja.

This track will trigger a northward surge of low-level moisture up the GoC. Models are typically slow on these surges, and I expect the surge will reach into southwestern Arizona tomorrow night or Thursday morning. Hopefully, the increased low-level moisture will help get thunderstorm activity going again. Note that this morning's TWC sounding data indicate only 0.79" of PW and no CAPE, but with a very deep layer of east-northeast winds of 30 to 40 kt.

Satellite views of Genevieve this morning: IR above from 5:30 am and visible below from about 6:30 am. This is certainly the most impressive storm so far this season in the Eastern Pacific.

Forecast of PW above is from the 00 UTC WRF-GFS on the 5.4 km grid and is valid at 5:00 am on Friday the 21st. As noted above, I suspect the moisture surge will occur sooner than model forecasts.

Finally, I show the GEFS plumes for QPF from 00 UTC last evening, showing how markedly different the operational GFS is from the rest of the ensemble members.

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