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Lixion A. Avila and Jamie Rhome

the first tropical storm, with the formation of Tropical Storm Alvin on 27 May, immediately followed by the formation of Tropical Storm Barbara on 29 May. The long-term (1971–2006) median start day is 29 May. No other named cyclone developed until the depression that eventually became Hurricane Cosme formed on 14 July. Flossie was the only major hurricane of the season and the intensification occurred just before it entered the central Pacific hurricane basin at 140°W. Using analysis techniques

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James L. Franklin, Lixion A. Avila, John L. Beven II, Miles B. Lawrence, Richard J. Pasch, and Stacy R. Stewart

storms, three fewer than normal, formed during this period. While sea surface temperatures were at or above normal over most of the basin during this time, atmospheric conditions appear to have been less favorable. Figure 2 shows the monthly anomalies of 200–850-mb vertical wind shear for the months of August and September, calculated using twice-daily analyses from the National Oceanic and Atmospheric Administration (NOAA)/National Weather Service's Global Forecast System (GFS) and long-term means

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Edward N. Rappaport

seasonal hurricane frequency: El Niño and 30 mb quasi-biennial oscillation influences. Mon. Wea. Rev., 112, 1649–1668. Hebert, P. J., and K. O. Poteat, 1975: A satellite classification technique for subtropical cyclones. NOAA Tech. Memo. NWS SR-83, Fort Worth, TX, 23 pp. [NTIS COM 75-11220/AS.] . Jarvinen, B. R., and C. J. Neumann, 1979: Statistical forecasts of tropical cyclone intensity for the North Atlantic basin. NOAA Tech. Memo. NWS NHC-10, 22

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John L. Beven II, Lixion A. Avila, James L. Franklin, Miles B. Lawrence, Richard J. Pasch, and Stacy R. Stewart

eastern North Pacific basin. Tropical Cyclone intensity estimates can be obtained from the imagery using the Dvorak (1984) technique. Such estimates, or “classifications,” are provided every 6 h by the Tropical Analysis and Forecast Branch (TAFB) of the Tropical Prediction Center, the Satellite Analysis Branch of the National Environmental, Satellite, Data, and Information Service (NESDIS), and the Air Force Weather Agency. Geostationary satellites are also the source for wind vectors derived from

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Lixion A. Avila, Richard J. Pasch, John L. Beven II, James L. Franklin, Miles B. Lawrence, and Stacy R. Stewart

and applying the Dvorak (1984) technique. Aerial reconnaissance is rare in this basin. In fact, the only reconnaissance flight in 2004 was conducted by the 53rd Weather Reconnaissance Squadron, the “Hurricane Hunters” of the U.S. Air Force Reserve Command (AFRC) during Tropical Storm Lester when the cyclone was near land. A description of the various observational data sources utilized to track tropical cyclones in this basin is given by Avila et al. (2003) . More information about each named

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Lixion A. Avila and John L. Guiney

” database 1 specifies center position, the maximum 1-min sustained surface wind speed, and the minimum sea level pressure. These parameters are estimated at 6-h intervals based upon poststorm analysis of all available data. The primary sources for the analysis are the National Oceanic and Atmospheric Administration (NOAA) Tropical Analysis and Forecast Branch collocated with the NHC, the NOAA Satellite Analysis Branch, and the Air Force Weather Agency. These centers provide the NHC with real

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Richard D. Knabb, Lixion A. Avila, John L. Beven, James L. Franklin, Richard J. Pasch, and Stacy R. Stewart

). Analysis of 200-mb-velocity potential anomalies ( Fig. 3 ) indicates that the extended periods without tropical cyclones coincided with the upper-level convergence phases of the MJO over the tropical eastern North Pacific. Conversely, periods dense with activity tended to occur during the upper-level divergence phases, although no tropical cyclones formed during the upper-level divergence phase in early June. Using satellite data analysis techniques described by Avila et al. (2003) , the genesis of

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Richard J. Pasch, Eric S. Blake, Lixion A. Avila, John L. Beven, Daniel P. Brown, James L. Franklin, Richard D. Knabb, Michelle M. Mainelli, Jamie R. Rhome, and Stacy R. Stewart

28 August). Using satellite data analysis techniques described by Avila et al. (2003) , the genesis of most of the tropical cyclones in the eastern North Pacific during 2006 can be attributed, at least in part, to westward-moving tropical waves that originated from Africa and crossed Central America. These tropical waves, with their focused source of low-level vorticity, propagated into the eastern North Pacific throughout the hurricane season as usual. However, they led to the development of

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James L. Franklin and Daniel P. Brown

, but does not include remnant low or extratropical stages. For storms east of 55°W, or those not threatening land, the primary (and sometimes sole) source of information is geostationary weather satellite imagery, interpreted using the Dvorak (1984) or Hebert–Poteat ( Hebert and Poteat 1975 ) techniques. Ships and buoys occasionally provide important in situ observations on these cyclones. For systems posing a threat to land, in situ observations are also generally available from aircraft

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Michael J. Brennan, Richard D. Knabb, Michelle Mainelli, and Todd B. Kimberlain

tropical cyclone reconnaissance. Bull. Amer. Meteor. Soc. , 82 , 567 – 578 . Hebert , P. J. , and K. O. Poteat , 1975 : A satellite classification technique for subtropical cyclones. NOAA Tech. Memo. NWS SR-83, 25 pp. [Available from National Weather Service, Fort Worth, TX 76102] . Jarvinen , B. R. , and C. J. Neumann , 1979 : Statistical forecasts of tropical cyclone intensity for the North Atlantic basin. NOAA Tech. Memo. NWS NHC-10, 22 pp . Kalnay , E. , and Coauthors , 1996

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