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Pacific ENSO Update

2nd Quarter, 2011 Vol. 17 No. 2


Tropical cyclone activity in the western North Pacific during 2011 is expected to rebound from the record-setting inactivity experienced during 2010. From January 2011 through mid-April of 2011, there have been some episodes of westerly winds along the equator extending eastward to near 150°E accompanied by the formation of large areas of disturbed weather. During the progress of one such episode of westerly winds along the equator in early April, the JTWC numbered two tropical depressions: TD 01W, which formed in the South China Sea and later dissipated there; and TD 02W, which emerged from a low-latitude monsoon depression centered near Palau. TD 02W slowly consolidated northeast of Palau, and then tracked to the northeast on a path taking it to the north of Guam and Saipan. Surface winds on Guam and Saipan became westerly for a few days as TD 02W passed to the north. The only adverse weather noted during the passage of TD 02W through Micronesia was some high surf on western shores noted particularly at Yap and Palau. TD 01W and TD 02W were not named by the JMA, so the basin still stands with no named TCs through mid-April.

The Southern Hemisphere cyclone season of 2010-2011 has been below average, particularly in the South Indian Ocean. Most of the southern Hemisphere TC activity has been in the Australian regions of the South Pacific and South Indian Ocean. This is consistent with La Niña, and was anticipated in earlier PEAC forecasts, and forecasts made by the Australian Bureau of Meteorology. TC activity east of the International Date Line has been reduced overall, with one notable storm occurrence: Tropical Cyclone Wilma (TC 08P). TC Wilma passed very near to Pago Pago on 24 January 2011 as a minimal hurricane with little impact in the region. The total of 21 TCs numbered by the JTWC in the Southern Hemisphere from July 2010 through mid-April 2011 is below normal. In fact, through 21 April 2011, the Southern Hemisphere Accumulated Cyclone Energy (ACE) (see was sitting at 140.4 versus a normal for the season to date of 210, or 67%. ACE is a measure of tropical cyclone activity that takes into account the intensity and duration of storms. No further TC activity is anticipated for American Samoa through June 2011 to finish out the current cyclone season.

The PEAC Center archives western North Pacific tropical cyclone numbers, track coordinates, and 1-minute average maximum sustained wind taken from operational warnings issued by the Joint Typhoon Warning Center (JTWC) of the U. S. Air Force and Navy, located at Pearl Harbor, Hawai'i. Western North Pacific tropical cyclone names are obtained from warnings issued by the Japan Meteorological Agency (JMA), which is the World Meteorological Organization's Regional Specialized Meteorological Center (RSMC) for the western North Pacific basin. The PEAC archives South Pacific tropical cyclone names, track coordinates, central pressure, and 10-minute average maximum sustained wind estimates from advisories issued by the Tropical Cyclone Warning Centers at Brisbane, Nadi, and Wellington. The numbering scheme and the 1-minute average maximum sustained wind estimates are taken from warnings issued by the JTWC. There are sometimes differences in the statistics (e.g., storm maximum intensity) for a given tropical cyclone among the agencies that are noted in this summary.

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Page Last Modified: August 04 2011 22:00:29 GMT


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