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Pacific ENSO Update

4th Quarter, 2011 Vol. 17 No. 4


After a substantial rebound of tropical cyclone activity in the western North Pacific through September 2011, the basin activity entered an odd state of near collapse as La Niña became reestablished in October 2011. Through the end of October, the JTWC numbered 23 tropical cyclones in the western North Pacific Basin with the JMA providing names for 20 of these. This is now below normal. The eastern North Pacific has had 12 cyclones numbered by the National Hurricane Center (Miami), with 10 of these named. During 1979 through 2000 there were typically 18 named tropical cyclones in the eastern North Pacific, a statistic that has now fallen to 15.6 (when the 30-year averaging period is shifted to include the recent quiet decade of the 2000’s). The central North Pacific has had no named tropical cyclones.

A recently released summary of TC activity in the western North Pacific provided by Paul Stanko, the senior forecaster at the Guam WFO, includes TS Banyan (23W), which lasted from 10 October to 14 October. Banyan spun up in the Republic of Palau and was first named to the west of Koror in the Philippine Sea. It moved west-northwestward most of its life, crossing over extreme northern Mindanao and several of the Visaya islands in the Philippines. It then turned north and dissipated over open water, never exceeding the 35 knot threshold for a minimal tropical storm. Although we have not yet had a 24W, it is worth noting that the Very-Early, Early and Near-Normal quintiles windows have closed. So, 24W will be either in the Late or Very Late categories this year. So far this year, our activity versus normal for 7 October is: (1) Numbered tropical cyclones (TD or higher): 23 vs. 26.42 or 87.1% of normal (was 94.0% on Oct 7), (2) Named tropical cyclones (TS or higher): 19 vs. 22.91 or 82.9% of normal (was 88.9% on Oct 7), (3) Typhoons or higher: 11 vs. 14.79 or 74.4% of normal (was 85.5% on Oct 7), (4) Super Typhoons (130 kt or more): 4 vs. 3.47 or 115% of normal (was 134% on Oct 7).

For the remainder of the season, Paul Stanko provides the following forecast: The regression forecast is for 28 significant tropical cyclones, which is in the Below-Normal quintile. (The previous forecast on 7 October was for 30 TC's, as was the forecast on 28 August, which is in the Near-Normal quintile). The R^2 for this regression is 0.915. The 95% confidence interval is now 23 to 32 TC's inclusive, with all past forecasts and re-forecasts falling within the 95% confidence interval. Note that we can no longer be 95% confident that we will have at least one more TC!

The Southern Hemisphere cyclone season of 2011-2012 will start soon. From 01 July 2011 to date, there have been no numbered tropical cyclones in the Southern Hemisphere. Activity in the Southern Hemisphere usually begins to trend upward in November with a long-term average of 1.5 cyclones experienced during November and 33 in December. The peak month for Southern Hemisphere tropical cyclones is February with a long-term average of 6.6 numbered cyclones. The Australian Bureau of Meteorology (BoM) issued the following outlook for the 2011-12 South Pacific Seasonal Outlook for Tropical Cyclones:

“The outlook for the 2011-2012 tropical cyclone season calls for a westward shift in tropical cyclone activity. This season there is a 65% chance that the Western Pacific Region [Coral Sea] will see more than the average number of tropical cyclones (35% chance of fewer than average) and a 40% chance that the Eastern Pacific Region [encompassing American Samoa] will see above average number (or a 60% chance that fewer cyclones will form). This outlook is based upon the status of the El Niño - Southern Oscillation (ENSO) over the preceding July to September period. During this period in 2011, neutral to borderline La Niña conditions were present. Historically, these conditions have favored a westward shift in tropical cyclone activity in the South Pacific.”

The Australian Bureau of Meteorology (BoM) is also predicting an above average number of tropical cyclones for all regions across northern Australia during the 2011-2012 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: December 07 2011 03:17:39 GMT


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