Skip Navigation Links 
NOAA logo - Click to go to the NOAA home page National Weather Service   NWS logo - Click to go to the NWS home page
Climate Prediction Center

HOME > Expert Assessments > Climate Diagnostics Bulletin

Tropical Highlights - April 2000

Oceanic cold episode conditions have weakened across the tropical Pacific during the past few months, but the atmospheric circulation continues to reflect mature cold episode conditions. Sea surface temperatures (SST) remained more than 1.0C below normal across the central equatorial Pacific between 160E and 160W (Fig. T18). However, above-average SSTs were observed in the eastern Pacific during April (Fig. T18, Table T2). The SST indices in all four Nio regions increased during April (Table T2), with positive indices recorded in the Nio 1+2 region for the first time since March 1999, and in the Nio 3 region for the first time since May 1998 (Fig. T5).

The oceanic thermocline remained much deeper than normal in the west-central and western Pacific during April and also deepened in the eastern Pacific (Fig. T15). In the west oceanic temperatures were more than 5.0C above normal during April at thermocline depth (Fig. T17). Across the east-central and eastern Pacific, the deepening thermocline has resulted in a lessening of negative temperature anomalies at thermocline depth, with temperatures more than 2.0C below normal observed only between 110W and 140W during the month (Fig. T17).

The pattern of tropical convection during April [as inferred from anomalous outgoing longwave radiation (OLR)] remained consistent with ongoing cold episode conditions, and featured suppressed convection over the western and central equatorial Pacific and enhanced convection over Indonesia and the Indian Ocean (Fig. T25). This pattern has persisted since the onset of cold episode conditions in late May 1998 (Fig. T8). Elsewhere, the Atlantic ITCZ was enhanced from northeastern Brazil to southwestern Africa during the month (Fig. T25).

The pattern of tropical convection over the central and western Pacific was again accompanied by an enhanced Walker circulation across the central equatorial Pacific (Fig. T29), with low-level (850 hPa) easterly wind anomalies across the central and western tropical Pacific greater than 6 m s-1 between 140E and 170W (Fig. T20). At upper-levels (200-hPa), troughs were observed over the low-latitudes of the central Pacific in both hemispheres, with amplified subtropical ridges dominating most of the remainder of both hemispheres (Fig. T22).

The sea level pressure (SLP) pattern across the Tropics during April featured positive anomalies across the tropical central and eastern Pacific and negative anomalies over the Indian Ocean and Indonesia (Fig. T19). This pattern is consistent with ongoing cold episodes, and was associated with positive values of both the Southern Oscillation Index (1.2)(SOI) (Table T1, Fig. T1) and the equatorial SOI (2.2) (Fig. T2).

NOAA/ National Weather Service
NOAA Center for Weather and Climate Prediction
Climate Prediction Center
5830 University Research Court
College Park, Maryland 20740
Page Author: Climate Prediction Center Internet Team
Page last modified: August 24, 2007
Information Quality
Privacy Policy
Freedom of Information Act (FOIA)
About Us
Career Opportunities