for the afternoon, Ants Leetmaa, director of the Na- storms than would occur in a normal year, the south- tional Oceanic and Atmospheric Administration/Na- east will have more tornadoes, and there will be fewer tional Center of Environmental Prediction's (NOAA/ hurricanes. In La Nina years, there might be flooding NCEP) Climate Prediction Center (CPC). Leetmaa's in North Dakota, and a more active hurricane season talk was titled "Forecasting for Social and Economic and intense ice storms in the northeast. Benefits: Linking Climate and Weather Services." Leetmaa said that in its "Vision for 2001 and Be- According to Leetmaa, the exceptional El Nino- yond," NWS states that it hopes to increase use of and La Nina-induced weather over the last two years physics-based modeling in the prediction process and has changed the way we look at climate and has made hopes to increase the certainty/confidence of the pre- us focus more sharply on which weather phenomena dictions. To do this, NWS will implement a suite of we can and cannot forecast. The National Weather Ser- forecast products that link weather and climate and vice (NWS) is headed toward maximizing the mitiga- increase lead times in order to enhance mitigation. tion of natural disasters as well as examining the —Lauraleen O'Connor. negative and positive economic benefits. Prior to 1997, El Nino forecasts were characterized by low confi- Central Gulf Coast dence with marginal skill and small lead times. How- The chapter met on 8 February 1999 to hear a talk ever, the 1998-99 El Nino and La Nina events were by Jeff Hawkins of the Naval Research Laboratory in characterized by high confidence with record predic- Monterey, California. Hawkins is noted for a Navy tion skill and long lead time based on extensive re- Meritorious Civilian Service Award received in 1999 search. In addition, for the first time NWS issued social for his contributions to the navy's operational meteo- and economic threat statements months in advance. rological support. Leetmaa said that through the NWS Field Office Pub- Hawkins talk was titled "Overview of Tropical lic Outreach Programs, NWS encourages the public to Cyclone Reconnaissance." It was an overview of air- pay attention, prepare, and act to mitigate impacts. borne and satellite techniques used to locate, track, and Leetmaa pointed out that El Nino and La Nina analyze tropical cyclones from 1945 to the present. events have occurred for thousands of years. They Hawkins said that during the 1940s, tropical cyclone occur when a shift in the temperature of the tropical hunters had to visually estimate the wind and storm Pacific Ocean leads to a shift in precipitation patterns. strength while flying below cloud base at 300-770-ft Coupling models, which capture the changes in both flight altitudes. Without the current Global Position- the atmosphere and ocean, has led to increased skill ing System (GPS) capabilities, tropical cyclone recon- in predicting these events. Leetmaa said there are four naissance in the early days was very hazardous, markers/indicators used in the statistical models to pre- difficult, and uncomfortable. Hawkins explained that dict these events: the global temperature index, the today, a combination of C-130s, P-3s, and the new Gulf Stream aircraft use GPS, dropsondes, and mul- tropical ocean warm pool index, the El Nino-South- ern Oscillation (ENSO, Nino 3.4) index, and the Arc- tic oscillation (AO) pressure index. The U.S. temperature and precipitation trends can be described effectively by two out of four of these indices. The temperature trend is almost entirely described by the warm pool index, while the precipitation trend is best described by the warm pool and AO indices. Leetmaa explained that El Nino event forecasts gen- 588 Douglas L. Sheadel 1999 erally require more skill than forecasts for La Nina 589 Douglas K. Lilly 1999 events. This is due to the fact that while El Nino years 590 Marsha C. Kinley 1999 are very different from normal years, La Nina years 591 Loren C. Marz 1999 are not normal, but they are not far off from normal. 592 Byron L. Marler 1999 The public responds to historical, actual data rather 593 Stephen P. Pryor 1999 than to statistics and averages, so NWS presents the 594 Shane D. Mayor 1999 predictions in terms of deviations from a normal/typi- cal year rather than to a mean year. For example, in El Nino years, California will have more intense winter 99 7 Bulletin of the American Meteorological Society
Bulletin of the American Meteorological Society – American Meteorological Society
Published: May 1, 1999
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