Wednesday, May 16, 2012

Tropical Weather Season Officially Underway in the Pacific...

As mentioned in a post on Monday, Tropical Storm Aletta apparently didn't get the memo concerning the "official" start of the tropical weather season in the North Pacific, which was yesterday, May 15th.  The system became the first disturbance of the season on Monday morning, and was named Tropical Storm Aletta within 24 hours.

The good news is that Aletta does not pose any threat to land.  Another area of disturbed weather bears watching a couple of hundred miles to the East of Aletta, and may become the second organized disturbance of the season soon. 

Due to colder water temperatures and an unfavorable middle and upper level wind flow pattern, tropical systems that form in the Pacific rarely make landfall in the U.S.  The map below shows the tracks of each of the systems that formed in the Eastern North Pacific in 2011, and this is typical of what we see in any given year:

As you can see, the vast majority of the systems diminished even prior to nearing Hawaii, which is also typical of the situation.  

Since records have been kept, a tropical cyclone has made direct landfall in California only one time, on September 25, 1939.  Tropical Storms and hurricanes were not officially "named" at that time, so this one was later dubbed the "1939 Long Beach Tropical Storm".  Most of the damage was caused due to storm surge and fresh water flooding, as wind gusts only averaged 50-60 mph.

Arizona (especially Southern parts of the state) occasionally observes Tropical Storm force winds and rain associated with a hurricane that diminishes after making landfall in Mexico.

Sometimes the southwestern U.S. (including Texas) benefits from some of the rainfall produced by a system that makes landfall in Mexico.  The trick in this situation is that the moisture has to survive a trip across the very rugged mountain terrain to the immediate North before reaching the U.S.

Below is the list of names for the 2012 Tropical Storm and Hurricane season in the Eastern North Pacific basin:


Remember that in both the Pacific and Atlantic basins, a system becomes "named" when it reaches Tropical Storm or Hurricane strength.  Tropical Depressions are given a number.

In case you'd like a brief 
refresher course, below is how things typically progress in the tropics (Pacific or Atlantic) as far as the formation and classification of a system are concerned: 

(1). Tropical Wave - developing area of low pressure where thunderstorms are still relatively disorganized.  No real center or sustained wind field.  A name or number is not formally assigned to this type of system, however it may eventually be given an "Invest" (or area of investigation) number as it develops further.

(2). Tropical Depression - developing area of low pressure with more organized thunderstorm activity.  Develops an area with sustained winds of 38 mph or less.  A number is assigned to the system once it reaches this stage (i.e., Tropical Depression One, Two, Three, etc.)

(3). Tropical Storm - organized area of low pressure & thunderstorm activity with sustained winds of 39-73 mph.  A formal name is given to the system at this stage.

(4). Hurricane - organized area of low pressure & thunderstorm activity with sustained winds greater than 73 mph.  Continues with the same name assigned once it reached Tropical Storm strength.

Once a storm reaches Hurricane strength, it is also assigned an intensity on the "Saffir-Simpson Scale" (similar to the EF-scale used for tornadoes).  For more on the Saffir-Simpson Scale, see this post.

Please view this post for a complete rundown of tropical weather safety and preparedness tips, as well as information on the differences between various tropical weather watches and warnings.

As I always like to point out, there is no reason to fear a particular severe weather season if you are prepared.  Taking a few minutes right around the start of the season, followed by a "refresher" course every once and awhile throughout the season will keep you up to date and prepared in the event that a system threatens your area.

The official start of the tropical season in the Atlantic is June 1.  Look for another post regarding tropical characteristics, storm names, etc. for that basin around that time.

For more information, including "live blogging" during rapidly changing weather events, please be sure to follow me on facebook and/or twitter:


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