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February 11, 1998

Very strong warm episode (ENSO) conditions continued during January 1998, as tropical Pacific sea surface temperatures (SSTs) remained well above normal east of the date line (Fig. 1, bottom). Actual SSTs in the eastern Pacific increased during the month, as SSTs greater than 28.0°C (the threshold for deep tropical convection and heavy precipitation) extended across the entire equatorial Pacific (Fig. 1 , top). SST anomalies exceeded +2.0°C over the equatorial Pacific east of 170°W and +4.0°C from 135°W eastward (Fig. 1, middle), while anomalies in the eastern equatorial Pacific decreased during the month. This decrease does not indicate a weakening of the El Niño episode. Instead, it reflects the normal annual cycle, which produces sharp increases at this time of the year in the climatological mean SSTs that are used as the basis for computing anomalies (Fig. 2).

Tropical precipitation during January was again greatly enhanced across the central and eastern equatorial Pacific, and suppressed over Indonesia and the western Pacific (Fig. 3). This overall pattern has persisted since June 1997, with the maximum in enhanced precipitation located between 160°W and 130°W since November. Precipitation has also been greatly suppressed over the eastern Indian Ocean and enhanced over the western Indian Ocean and eastern Africa, where rainfall surpluses since October exceed 1000 mm (40 inches) in some parts of Kenya.

The strong ENSO conditions in the tropical Pacific contributed to pronounced departures from normal in the position and intensity of the jet stream over the North Pacific and North America during January (Fig. 4 ). The Pacific jet stream during January remained strong across the entire North Pacific from south of Japan to just off the California coast (Fig. 4, bottom). As this pattern developed during the month, storminess increased in intensity and frequency over the eastern North Pacific and over the west coast of the United States. This pattern intensified further during the first week of February contributing to very heavy precipitation over most of California. The main core of the jet stream then continued eastward over northern Mexico and over the Gulf of Mexico, where a series of intense low pressure systems developed from mid-January through the first week of February. Precipitation was especially heavy along the immediate Gulf Coast, over Florida and throughout the Southeast and Mid-Atlantic. Precipitation since the beginning of November ranged from 375-500 mm (15-20 inches) greater than normal in sections of California and the Gulf Coast states (Fig. 5).

Based on current conditions in the tropical Pacific and on the NCEP SST predictions, we expect warm episode (ENSO) conditions to continue through the northern spring. As a result, the above circulation features are likely to continue over North America through March, and possibly into April. Impacts of these conditions are likely to be recurring periods of significant storm activity and precipitation across California and the southern tier of the United States, and continued milder-than-normal conditions over much of central North America. Globally we expect drier-than-normal conditions over Indonesia, northern Australia, northern South America, and southern Africa, while wetter-than-normal conditions can be expected over the central and eastern equatorial Pacific, along the coasts of Ecuador and northern Peru and over southeastern South America.

Weekly updates for SST, 850-hPa wind, and OLR are available on the Climate Prediction Center homepage at: http://nic.fb4.noaa.gov/.

Climate Prediction Center
National Centers for Environmental Prediction
NOAA/National Weather Service
World Weather Building
Washington, D.C. 20233
e-mail: wd52vk@hp31.wwb.noaa.gov

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