1. 4B.2 A comparison of typhoon best-track data in the western North Pacific: irreconcilable differences. by Mark A. Lander University of Guam Central Guam mountains after a major brushfire.

2. The two primary agencies responsible for basin-wide TC coverage — the Joint Typhoon Warning Center (JTWC) and the Japan Meteorological Agency (JMA) — are so incompatible as to call into question the utility of their best-track TC data for climate studies. The Joint Typhoon Warning Center (JTWC), now located in Pearl Harbor, Hawaii, has a nearly 50-year record of tropical storms and typhoons for the western North Pacific Basin. The JTWC is jointly manned by the U.S. Navy and U.S. Air Force to provide tropical cyclone reconnaissance and forecast support to the U.S. Military and other U.S. Government agencies and assets in the eastern Hemisphere. The JTWC has a continuous record of tropical cyclone activity in the western North Pacific extending from 1959 to present. Until the year 2000, it also provided the names for the TCs of that basin.

3. P. J. Webster, G. J. Holland, J. A. Curry, H.-R. Chang Science 16 September 2005:Vol. 309. no. 5742, pp. 1844 – 1846 Examination of hurricane intensity shows a substantial change in the intensity distribution of hurricanes globally. The number of category 1 hurricanes has remained approximately constant but has decreased monotonically as a percentage of the total number of hurricanes throughout the 35-year period. The trend of the sum of hurricane categories 2 and 3 is small also both in number and percentage. In contrast, hurricanes in the strongest categories (4 + 5) have almost doubled in number (50 per pentad in the 1970s to near 90 per pentad during the past decade) and in proportion (from around 20% to around 35% during the same period). These changes occur in all of the ocean basins. True if one uses JTWC False if one uses JMA !!!

4. In General: JTWC intensities too high !! OR JMA intensities too low !!

5. 1996 Typhoon Season Wind speed difference (kt)

8. Why ?? JTWC uses 1-minute average for sustained wind speed. JMA uses 10-minute average for sustained wind speed. Difference between 1-min and 10-min is approximately 115%.

9. Why ?? JTWC and JMA use different T-number conversion tables. Dvorak T number/wind speed comparison T Number JTWC JMA 10 to 1 2 30 30 33.6 2.5 35 35 39.2 3 45 45 50.4 3.5 55 55 61.6 4 65 65 72.8 4.5 77 70 78.4 5 90 77 86.2 5.5 102 85 95.2 6 115 93 104.2 6.5 127 100 112.0 7 140 107 119.8 7.5 155 115 128.8 8 170 122 136.6 JMA can’t get CAT 5 until T8 is reached !!

12. Who is right ??? Anecdotal Evidence. Investigate individual TCs

13. Tropical Storm Greg (43W 96)

14. Strongest Westerly Wind Burst ever Observed ! (December 1996)

16. Impacts of TS Greg 1996 JTWC Annual TC Report “Greg was responsible for loss of life and extensive damage to property in the East Malaysian State of Sabah (located on the northwest coast of Borneo). At least 124 lives were reported lost with another reported missing primarily due to flooding from torrential rains. In Kota Kinabalu, The capital of the State of Sabah, high wind scattered billboards and other debris, and broke windows in the 30-story government building.”

17. Typhoon Vamei Typhoon Vamei. Microwave image courtesy of NRL Monterey: (http://www.nrlmry.navy.mil/tc_pages/tc_home) JTWC: 75 kt JMA 45 kt

18. JTWC Annual Tropical Cyclone report for 2001: “At 270000Z, JTWC classified the system as a typhoon based on naval ship observations indicating sustained winds within the small eyewall of 75 knots with gusts to 105 knots.”

19. Even today problems persist. October 2007: Two midget typhoons Haiyan Podul

21. Midget typhoon Haiyan JTWC: No Warning. 20 kt on ABPW JMA: 40 kt.

22. TC Podul (Midget Typhoon) JTWC: No Warning. 20 kt on ABPW JMA: 55 kt

23. Annual comparisons Here it gets messy.

24. 1996 Typhoon Season Wind speed difference (kt)

33. Conclusions: (1) The differences of wind intensities between the JTWC and the JMA are irreconcilable. There is no uniform or physically meaningful correction that can be applied to the two data sets to bring them into line with each other. (2) Establish a working group of tropical cyclone diagnostic experts to undertake a project similar to the HRD Hurricane Reanalysis Project for the historical record of the tropical cyclones of the western North Pacific.