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Pacific ENSO Update

2nd Quarter, 2011 Vol. 17 No. 2


Based on available guidance1 and the forecast behavior of ENSO, the PEAC tropical cyclone outlook for the upcoming western North Pacific typhoon season of 2011 is for near normal activity, notwithstanding the recent widespread trend toward reduced numbers of TCs. There may be a notable westward shift of TC activity in the first half of 2011 as the waning La Niña still exerts some influence on the weather of Micronesia. By fall of 2011, under a scenario of ENSO-neutral conditions, the TC activity in the western North Pacific (and in Micronesia) should be close to normal for cyclone numbers and cyclone formation locations and tracks (see island summaries for further details).

On March 8, 2011, the Tropical Storm Risk (TSR) Research Group ( issued the following assessment of tropical cyclone activity for the western North Pacific basin: “The TSR extended range forecast for Northwest Pacific typhoon activity in 2011 anticipates a season with activity close to normal. Based on current and projected climate signals, Northwest Pacific typhoon activity in 2011 is forecast to be double that seen in 2010 (which recorded the fewest number of tropical storms and typhoons since reliable records began in the mid 1960's). The forecast spans the period from 1st of January to 31st of December 2011 (95% of typhoons occur historically after the 1st of May). ... Updated forecasts will be issued in early May, early July, and early August.”

Intense Typhoons*
7.8 (+ 2.7)
17.5 (+ 3.3)
27.8 (+ 4.2)
46yr Climate Norm
8.5 (+ 3.0)
16.4 (+ 3.8)
26.3 (+ 4.6)
Note: (mean + SD); * One-Minute Sustained Wind > 95 kts

As of mid-April 2011, experimental forecasts for the annual total of western North Pacific TC activity issued by Paul Stanko (Senior forecaster, Guam WFO) indicate that the most likely category of 2011 TC activity is “normal,” (among seven groupings ranging from “record high” to “record low.”) These forecasts are based only on year-to-date activity, and are not very skillful this early in the season. The latest TC outlooks and forecast updates from Paul Stanko, the TSR, and the City University of Hong Kong Laboratory for Atmospheric research will be provided in the 3rd Quarter Newsletter due in mid-July.

1The PEAC tropical cyclone forecasts for 2010 are provisional. The PEAC considers input from three seasonal outlooks for tropical cyclone activity in the western North Pacific basin: (1) The City University of Hong Kong Laboratory for Atmospheric Research, under the direction of Dr. J. C-L. Chan; (2) The Benfield Hazard Research Centre, University College London, Tropical Storm Risk (TSR) research group, UK, led by Dr Adam Lea and Professor Mark Saunders (; and, (3) an experimental typhoon outlook produced by Paul Stanko (forecaster at the Guam WFO).

Pacific ENSO Applications Climate (PEAC) Center
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Page Last Modified: August 04 2011 21:55:05 GMT


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