The Tropics Are Coming to the Southwest

Three days ago we discussed the possibility of a major monsoon surge into the Great Basin (see Intricacies of Medium Range Monsoon Forecasts).  The large-scale pattern producing that surge now looks as if it will deliver in spades to the Southwest US and Northwest Mexico over the next several days in the form of not only the surge, but also the tracking of Hurricane Hilary along Baja California and then through SoCal after it has decayed into a tropical storm or depression.  

The GFS forecast shows the situation for 1800 UTC (1200 MDT) Sunday.  Hilary is off the Baja California Coast.  Tropical moisture in the form of a Monsoon Surge streams up the Gulf of California and into the Great Basin between an upper level trough along the Pacific Coast and a beastly ridge over the central US.  The latter has maximum 500-mb heights over 6000-m, which is quite high.  

This pattern persists through 1500 UTC (0900 MDT) Monday, with Hilary weakening but moving northward and affecting southern California, the monsoon surge persisting in the Great Basin, and monsoon moisture moving around the upper-level ridge into southern Canada.  

Thus, the impacts of this event stretch from Mexico to Canada.  

The GFS forecast for the Hilary storm center is on the west side of the potential track area forecast from the National Hurricane Center.  Their cone that illustrates the probable path of the storm center covers all of SoCal and the SoCal bight before extending up into northern California or Nevada.  Hilary is expected to be a hurricane through 12 AM Sunday, weaken to a tropical storm by 12 AM Monday, and then a depression as it continues northward.  

For northern Utah, much will depend on the location of the monsoon surge and the track of Hilary and her remnants.  I'll be keeping an eye on this and am interested to see what happens across the southwest US.