Saturday, September 29, 2018

WRF Forecasts Shift Rosa Track Eastward


The graphic above shows MIMIC TPW at 6:00 am MST this morning. Hurricane Rosa is near 20 degrees north, and now moving toward the north. PW values around 2 inches have now spread to nearly 30 degrees north, and will be increasing steadily late today and tomorrow over southern Arizona.

Plot below shows detected CG flashes over Mexico for 12-hours ending at 12 UTC this morning (from Atmo and Vaisala). Thunderstorms were active during the night and have spread northward into southern Sonora.


The synoptic pattern which will steer the decaying hurricane remains very complicated, as two waves at 500 mb interact and the western wave (now south of Aleutians) appears to be the one that will steer the remnants of Rosa across parts of Southwest. 

The local WRF forecasts (driven by the operational NAM and GFS) are forecasting a more eastward track than is NHC. The system is forecast to cross the northern GoC as a rapidly weakening depression. The situation remains very difficult wrt to possible rainfall amounts. The 06 UTC WRF  forecasts now indicate heaviest amounts in Arizona to occur over western Pima County and also over the mountains northeast of Phoenix. The forecast below is from the 06 UTC WRF-GFS and is valid for period ending at midnight on October 2nd. Compare with the forecast in previous post to get a feel for how much the forecast impacts of Rosa have shifted eastward.

As with many decaying tropical storms, the details of the forecasts for Arizona remain very difficult.

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