TROPICAL CYCLONE ACTIVITY

The PEAC 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, Hawaii. Western North Pacific tropical cyclone names are obtained from warnings issued by the Japan Meteorology 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.

Third Quarter 2007 Summary

The 2007 tropical cyclone season of the western North Pacific had been relatively quiet. Through October 15, the JTWC numbered only 18 tropical cyclones in the western North Pacific. The JMA named 16 of these. Two systems (Haiyan and Podul) were named by the JMA, but not carried by the JTWC. Of the 18 tropical cyclones numbered by the JTWC, the breakdown by intensity was: 11 typhoons (TY), 6 tropical storms (TS), and 1 tropical depression (TD). Normally there are approximately 22 tropical storms and typhoons (TS + TY) through October with a breakdown of 15 typhoons and 7 tropical storms. Four more typhoons and one tropical storm are needed by the end of October to bring 2007 back to a normal year (somewhat unlikely). In addition to a reduction in the annual number of tropical cyclones in the western North Pacific basin during 2007, the region of tropical cyclone formation was pushed well to the west and north of normal. Through mid-October 2007, no tropical cyclones formed south of 20°N and east of 160°E; a region designated as the “El Niño Box” by Lander (1994) (Fig. 2, below). Tropical cyclone formation is observed in the “El Niño Box” primarily during El Niño years and almost no tropical cyclones form in this region during non El Niño years .

Two named storms in the Central Pacific approached the Hawaiian Islands in the 3rd Quarter. On July 21, Tropical Depression Cosme passed 160 NM south of South Point on the Island of Hawaii , where there was no appreciable increase in the winds. Three weeks later on August 14-15, Hurricane Flossie approached the Hawaiian Islands, but turned west and quickly weakened to a tropical depression before passing south of the Big Island . No significant wind- or flood-related damages were reported from Flossie, although heavy surf caused minor coastal inundation problems on the Big Island.

Figure 2. The formation locations of the tropical cyclones of 1997 (triangles) and 2007 (black dots). The formation location of each tropical cyclone is defined as that point on the JTWC best track where the cyclone first acquired 25 kt wind speeds. Note the several tropical cyclones in the “El Niño Box” during the El Niño year of 1997, and the lack of tropical cyclone formation in this region during 2007 (a year evolving into La Niña).