Monday, April 18, 2011

Countdown to hurricane season begins

We are one getting closer to hurricane season every week. As of this afternoon, we are 26 days, 14 hours, and 46 minutes away from the start of the 2011 PHS. Th end of the season lasts 200 days, so we are 226 days, 14 hours, and 46 minuets away from hurricane season as well.

Now, we quote Dr. Steve Lyons with some EPAC climatology
"May 15th, is the start of the 2009 East Pacific hurricane season, about 2 weeks earlier than the Atlantic Basin hurricane season begins (June 1). Both end November 30th. These dates have been set to encapsulate well over 90% of tropical cyclones that form in each basin. On rare occasions we find development before each season "officially" begins and/or after the season "officially" ends. The last time we had an early start to the East Pacific hurricane season was in 1996 when a tropical depression formed on May 13th, two days before the official start dated; the following day it became the first tropical storm that year, and to this day remains nameless, the second tropical storm to form that year was named "Alma." It turns out that on-average the East Pacific is more active than the Atlantic Basin, and this is the case in most but not all years (2005 being the clearest recent example). Since the satellite era began in 1965 tropical cyclone annual averages are 16 tropical storms, 8 of those becoming hurricanes. Of particular interest is the fact that prior to being able to see tropical cyclones in this area of the world with weather satellites, many tropical cyclones were missed as this is not a typical high ship traffic area, hence weather reports from them have been historically sparse.

Tropical cyclone averages were 8 named storms, 3 of those becoming hurricanes in our historical record from 1949-1964. Yes, more than half of all tropical storms and two-thirds of hurricanes went undetected before the satellite era and very likely many ships got into much rougher weather than they were expecting! Prior to the satellite era that began around the time I was in 6th grade (1965), meteorologists had thought the Atlantic Basin was a far more active tropical cyclone region compared to the East Pacific. It is interesting how wrong we can be when we make assumptions without accurate information!

1949-1964 8 3

A large majority of tropical cyclone tracks are toward west of west-northwest and out to sea away from land. However each year is unique, some years have many more tracks that turn north and/or northeast toward land than other years. These track differences are related to changes in steering from one year to the next. El Nino years are more likely to see landfalls in Mexico and remnant tropical cyclones affecting California and the southwest U.S. Locations for formation of tropical cyclones in the East Pacific are the narrowest in the world, with a local maximum located near 15N latitude, 110W longitude.

The two most common U.S. impacts from East Pacific tropical cyclones are 1) high surf in Southern California from distant tropical storms and hurricanes and 2) flooding rains in the U.S. southwest that can at times spread across California and well into the central U.S. Surf can exceed twenty feet on south facing beaches of Southern California from swells coming from hurricanes offshore from Mexico. One year those swells were so high, some waves broke over the top of the Huntington Beach pier, the long-shore currents in the water were two to four miles per hour toward the north, and rip currents drown many beach goers. Flood disasters from remnants of tropical cyclones in California, Arizona, New Mexico and for that matter the entire southwest U.S. are too numerous to list. In 1939, one hurricane did not weaken over the cool California current as it headed toward that state. It made landfall near Long Beach and brought damaging tropical storm force winds, high surf and flooding rains. In 1972, Hurricane Hyacinth moved toward Southern California and although it weakened it struck San Diego as a tropical depression. So no, it is not impossible for California to be struck by a tropical storm, but it is rare, and far less rare for remnants of tropical cyclones to drift over Southern California and occasionally bring flooding rains in months that typically see no rain! I remember dancing in the street in heavy rains in the late summer of 1967 as hurricane "Katrina" moved up the Gulf of California and brought rains to San Diego and beyond. Yes, that was an interesting year with Hippies, Flower Children, motorcycle gangs and tropical cyclone remnants leaving their marks on my home state.
So before you head on that vacation to Baja, Mexico or Central America, check with The Weather Channel for any tropical cyclone threats that might affect you vacation destination. Oh and those of you in Southern California, you might win a party bet with that 1939 Long Beach landfall, just remember you are routinely vulnerable at the beach in high surf that can come from distant or not so distant East Pacific hurricanes.
The GFS storm we mentioned last week is turning into a modelstorm. Still, not bad for April.

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