Tropical Storm Hilary, Soon to Become Hurricane Hilary, Approaches California Sunday

Tropical Storm Hilary has officially developed today in the east Pacific. This will soon become Hurricane Hilary, as rapid intensification begins tonight. The National Hurricane Center expects Hilary to become a major hurricane on Thursday or Friday.

Hilary will weaken once it moves into cooler sea surface temperatures and higher upper level wind shear. The storm will steadily weaken, but in a slow enough rate to likely bring rain and breezy winds to much of California and other portions of the southwest. While it is highly unlikely it will remain a classic tropical storm as it approaches the coast-line, it will likely help to bring some much needed rain to the region, perhaps too much rain in some spots. Rain totals according to the weather prediction center are in the 1″ to 3″ range, with the potential for higher amounts depending on the storm track.

Hurricane history and California… The last hurricane to directly make landfall in California was in October of 1858, known as the San Diego Hurricane, estimated as a category 1. In September of 1939, a tropical storm made landfall officially in southwest California. There have been a number of decaying tropical systems bring rains to California over the years, as a remnant low pressure and surge of moisture, but all have lost the classic title of tropical storm or hurricane before reaching the coast.

Why is this so rare? The sea surface temperatures off the west coast are cold, due to the prevailing wind and ocean currents, which drives cooler waters down the west coast of the United States. The latest sea surface temperatures are in the general 66 to 69 degree range off the coast of California. For hurricane development, 80 degree or warmer sea surface temperatures are needed. According to NOAA, the sea surface temperatures near California are a few degrees below average, which will help to weaken the storm as it approaches.

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Richard Scott
WVUA Chief Meteorologist
rscott@wvua23.com
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