Initial Maintenance of Tropical Cyclone Size in the Western North Pacific
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Authors
Lee, Cheng-Shang
Chueng, Kevin K.
Fang, Wei-Ting
Elsberry, Russell L.
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2010-08
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Abstract
A tropical cyclone (TC) size parameter, which is defined here as the radius of 15 m s21 near-surface wind
speed (R15), is calculated for 145 TCs in the western North Pacific during 2000–05 based on QuikSCAT
oceanic winds. For the 73 TCs that intensified to typhoon intensity during their lifetimes, the 33% and 67%
respective percentiles of R15 at tropical storm intensity and at typhoon intensity are used to categorize small,
medium, and large TCs. Whereas many of the small TCs form from an easterly wave synoptic pattern, the
monsoon-related formation patterns are favorable for forming medium to large TCs. Most of these 73 TCs
stay in the same size category during intensification, which implies specific physical mechanisms for maintaining
TC size in the basin. The 18 persistently large TCs from the tropical storm to the typhoon stage mostly
have northwestward or north-northwestward tracks, while the 16 persistently small TCs eithermove westward–
northwestward in lower latitudes or develop at higher latitudes with various track types. For the large TCs,
strong low-level southwesterly winds exist in the outer core region south of the TC center throughout the
intensification period. The small TCs are more influenced by the subtropical high during intensification. The
conclusion is that it is the low-level environment that determines the difference between large and small size
storms during the early intensification period in the western North Pacific.
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Monthly Weather Review, Vol. 138, August 2010, pp. 3207-3223
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Meteorology
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This research is supported by the National Science Council and the National Applied Research Laboratories of the Republic of China (Taiwan). The participation of R. Elsberry was funded by the Office of Naval Research Marine Meteorology Division. Mrs. Penny Jones assisted in the manuscript preparation.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.