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Lixion A. Avila and Jamie Rhome

described by Avila et al. (2003) , most of the tropical cyclones formed from tropical waves that can be traced westward from the Atlantic basin into the eastern North Pacific. Figure 1 shows the shower activity associated with several tropical waves moving from the Caribbean Sea westward across Central America and into the eastern North Pacific. In particular, one can see the westward propagation of the convection associated with the wave that crossed Central America on 28 August. This wave was

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Lixion A. Avila and John L. Guiney

using satellite data. NOAA Tech. Rep. NESDIS 11, National Oceanic and Atmospheric Administration, Washington, DC, 47 pp. [Available from National Technical Information Service, U.S. Dept. of Commerce, Sills Bldg., 5285 Port Royal Road, Springfield, VA 22161.] . Molinari, J., D. Knight, M. Dickinson, D. Vollaro, and S. Skubis, 1997: Potential vorticity, easterly waves, and tropical cyclogenesis. Mon. Wea. Rev., 125, 2699–2708. ——, D. Vollaro, S. Skubis, and M. Dickinson, 1999: Eastern pacific

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John L. Beven II and James L. Franklin

landfall in 1999. Hurricanes Dora and Eugene crossed 140°W into the central Pacific basin, with Dora later crossing the international date line into the western North Pacific basin. One can speculate on the reasons for the inactive season. One possibility is the active 1999 Atlantic season ( Lawrence et al. 2001 ), which featured 16 tropical cyclones (TCs). Climatologically, most eastern North Pacific cyclones can be traced to disturbances (tropical waves) that cross Central America from the Caribbean

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

waves play a significant to dominant role in TC development in the eastern North Pacific Ocean. Avila et al. (2000) describe the methodology the NHC uses to track tropical waves from Africa across the tropical Atlantic, the Caribbean Sea, and Central America into the Pacific. Sixty-six tropical waves were tracked from the west coast of Africa across the tropical Atlantic and the Caribbean Sea from May to November 2003. Most of these waves reached the eastern North Pacific, where they played a role

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

North Pacific tropical storm is 2 June. Javier was the strongest hurricane of the season with peak winds of 130 kt. In addition to the 12 named cyclones in 2004, there were four tropical depressions that did not reach tropical storm status. One of them, Sixteen-E, made landfall in Baja California, Mexico. The formation of tropical cyclones from tropical waves in the eastern North Pacific has been documented in numerous occasions, for example, Avila et al. (2003) . Most of the tropical cyclones in

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

most of the tropical cyclones in the eastern North Pacific during 2005 can be attributed, at least in part, to one or more westward-moving tropical waves that originated from Africa and crossed Central America. The 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 more tropical cyclones during the upper-level divergence phases of the MJO, which provided an

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Edward N. Rappaport

wave’s “intrinsic” potential for development (e.g., its observed size, cloud and circulation structure, convective nature) when it crosses the west coast of Africa, and 2) the characteristics of the eastern Atlantic atmospheric and oceanic environment that it then encounters. While satellite signatures, surface pressure analyses, and circulation features derived from rawindsonde data provide some clues about tropical waves departing Africa, a reliable quantitative measure of point 1 above remains

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Lixion A. Avila, Richard J. Pasch, Jack L. Beven, James L. Franklin, Miles B. Lawrence, Stacy R. Stewart, and Jiann-Gwo Jiing

require the issuance of watches or warnings. Tropical wave records kept since 1967 indicate that most eastern North Pacific tropical cyclones are associated with westward-moving synoptic-scale disturbances, or tropical waves ( Avila and Guiney 2000 ). In general, these waves amplify and trigger tropical cyclones when they reach this basin, where climatologically favorable conditions for tropical cyclogenesis such as low-level cyclonic vorticity, high moisture, and low shear prevail ( Gray 1968 ). This

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

of the cyclone remained offshore. Hovmöller diagrams of twice-daily satellite images can be extremely useful in identifying the mode of tropical cyclogenesis in the eastern North Pacific. A recent illustrative example and discussion is provided by Avila et al. (2003) . These diagrams reveal that the genesis of half of the named storms in 2002 (Alma, Douglas, Elida, Fausto, Genevieve, and Iselle) could be clearly identified with Atlantic tropical waves traceable to the west coast of Africa. The

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