Forecast Forum - February 1999
The canonical correlation analysis (CCA) forecast of SST in the central Pacific
(Barnett et al. 1988, Science, 241, 192-196; Barnston and Ropelewski 1992, J.
Climate, 5, 1316-1345), is shown in Figs. F1 and F2. This forecast is
produced routinely by the Prediction Branch of the Climate Prediction Center. The
predictions from the National Centers for Environmental Prediction (NCEP) coupled
ocean/atmosphere model (Ji et al. 1998, Mon. Wea. Rev, 126, 1022-1034) are
presented in Figs. F3 and F4. Predictions from the Cane and Zebiak model (Cane et
al. 1986, Nature, 321, 827-832; Zebiak and Cane 1987, Mon. Wea. Rev.,
115, 2262-2278) are shown in Figs. F5 and F6. Predictions from the modified
Cane and Zebiak model (Chen et al. 1998, Geophys. Res. Let., 103,
2387-2840), referred to in the figures as LDEO3, are shown in Figs. F7 and F8.
Predictions using linear inverse modeling (Penland and Magorian 1993, J. Climate, 6,
1067-1076) are shown in Figs. F9 and F10. Predictions from the Scripps / Max Planck
Institute (MPI) hybrid coupled model (Barnett et al. 1993, J. Climate, 6,
1545-1566) are shown in Fig. F11.
The CPC and the contributors to the Forecast Forum caution potential users of
this predictive information that they can expect only modest skill.
Discussion and Outlook
Strong cold episode conditions continued in the tropical Pacific during February, as
sea surface temperatures (SSTs) remained well below normal across the central and
east-central equatorial Pacific (Fig. T18 and Table T2). Negative subsurface temperature anomalies and a
shallower than normal oceanic thermocline continue to dominate the equatorial Pacific east
of the date line (Figs. T16, T17).
The cooler-than-normal surface waters contributed to a vigorous Walker circulation over
the equatorial central Pacific (Fig. T29) characterized
by enhanced low-level easterlies (Fig. T20), enhanced
upper-level westerlies (Fig. T21 ) and suppressed
rainfall (Fig. E4) and deep convection over the
equatorial central Pacific (as inferred from Outgoing Longwave Radiation (OLR) measured by
NOAA's polar-orbiting satellites) (Fig. T25).
Given the strength and evolution of existing La Niņa conditions, we expect the cold
episode to continue for the next three to six months. This is supported by the latest NCEP
coupled model forecast (Figs. F3 , F4) which indicates that cold episode conditions
will continue through the boreal spring, followed by weakening cold episode conditions
thereafter. The NCEP statistical model forecast (Figs. F1, F2) is consistent with the NCEP coupled model through the spring,
but it suggests continued cold episode conditions through the remainder of the year. This
divergence between the NCEP forecasts also appears in other forecasts, and indicates the
considerable uncertainty in expected oceanic conditions during the second half of 1999.
Based on current conditions in the tropical Pacific, on the NCEP SST predictions, and
on results from historical studies on the effects of cold episodes, we expect
wetter-than-normal conditions to continue through March over Indonesia, northern
Australia, and southern Africa. Wetter-than-normal conditions are likely to develop over
Northeast Brazil and continue through May. Over the United States during the next three
months, drier- and warmer-than-normal conditions are expected in southern sections from
southern California eastward to the Carolinas. Wetter-than-normal conditions are expected
in the northern Great Plains and upper Midwest. Cooler-than-normal conditions are likely
over western and central Canada and Alaska.
Weekly updates for SST, 850-hPa wind and OLR are available on the Climate Prediction
Center homepage at: http://www.cpc.ncep.noaa.gov (Weekly Update).