Jimena Over Baja

Yesterday was a fairly down day across all of southern Arizona with post-MCS suppression west of here and periods of easterly downslope from Tucson east. There were some light showers and thunder across parts of the metro area but rain amounted mostly to sprinkles. Only 5 sites in the Alert network had rain; here at house there was both thunder and some sprinkles.

Jimena came ashore onto the Baja penninsula some time last night and appears to be over or west of the Baja spine this morning, as possibly a Cat 2 hurricane. Jimena will weaken rapidly today and probably move slowly north. The big change overnight is that the anticipated track of Jimena was drastically modified by NHC. The storm is now expected to drift west from Baja as an orphan low while the 500 cyclone moves north into the ridge before shearing apart over northern Mexico. Interestingly, the ECMWF operational model had indicated this for several runs now and has apparently won out over all the more sophisticated hurricane guidance models.

What will be Jimena's impacts here? Moisture continues to increase slowly across all of southern Arizona - PWs are now from 1.30 to 1.75" and high dewpoint air is coming across the border out across southwest Arizona. Middle-level temperatures are increasing along with the moisture increases, but there does appear to be some increase in CAPE today. The wind shear profile above 700 mb is reasonably favorable for strong storms, with lower level winds being light and variable. Cloud cover is increasing from the south and there appears to be an old shower band from Jimena east-west along about 30N. This feature is moving to the north also. Thus, the amount of sunshine and boundary layer heating may be limited by afternoon. Increases in low-level moisture would however increase CAPE rapidly - complicated situation, but I think that it's about a coin-toss for storms real rain today here at house.

Tomorrow and Friday are even more complicated, as the air mass transitions to a tropical one and the 500 mb Jimena circulation deforms across northern Mexico, essentially captured inside the expanding anticyclone. This is a very potent situation for heavy rains and the exact track of the Jimena remnants is hard to determine at this time. Careful monitoring definitely required through Friday morning. By the weekend, things are predicted to have returned to a typical summer pattern with ligering low-level moisture, before the next Pacific trough moves into the west coast.