Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 2:03 PM GMT on May 30, 2006
Hurricane season has begun in the Northeastern Pacific (the region off the west coast of Mexico), with the formation of Tropical Storm Aletta over the weekend. Aletta is expected to die by Thursday, a victim of high wind shear and dry air. At its peak, Aletta was only a weak tropical storm with top winds of 45 mph. The storm brought over two inches of beneficial rain to Acapulco, and ten inches to the surrounding mountains. Aletta is now moving away to the west over open ocean, bringing an end to the rains over Mexico.
Figure 1. Latest image of Aletta.
NOAA's 2006 forecast for the Northeastern Pacific hurricane season calls for a less active than usual year, with 12-16 named storms, 6-8 hurricanes, and 1-3 major Category 3 and stronger storms. On average, the Northeastern Pacific has 16 named storms, 9 hurricanes, and 4.5 major hurricanes. The pattern of upper level winds that favors an active hurricane season in the Atlantic typically brings high wind shear and low hurricane activity to the Northeastern Pacific. Last year's record breaking year in the Atlantic was balanced by a slightly below-average year in the Northeastern Pacific, which had 15 named storms, seven hurricanes, and two major hurricanes. The last three east Pacific hurricane seasons have been below normal, following an overall trend of lower activity since 1995. This is exactly the opposite of what has been observed in the Atlantic. "Since 1995, despite the trend to warmer waters in the tropical east Pacific, higher wind shear has contributed to fewer tropical storms, hurricanes, and major hurricanes," noted Muthuvel Chelliah, NOAA's Climate Prediction Center lead scientist on the east Pacific hurricane season outlook.
The Northeast Pacific basin hurricane season officially began May 15. The season has a broader peak than the Atlantic. Activity usually begins in late May or early June, and lasts until late October or early November. Peak storminess occurs in late August/early September. Only three Eastern Pacific hurricanes have had their names retired--Hurricane Ismael of 1995, Hurricane Pauline of 1997, and Hurricane Kenna of 2002, all of which hit Mexico. In addition, Adolph and Israel of 2001 had their names retired for political reasons.
I'll be back Wednesday with a look at Bill Gray's latest Atlantic hurricane season forecast, due to be issued tomorrow.
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