Friday, January 26, 2007

El Nino weakening, west Pacific convection not the answer

The following is a posting that was placed on the HMT Blog at

Please go to that link if you would like to see some figures.

An MJO excited deep convection near the date line in early January 2007 but a "combined" Pacific jet and eastward shifted storm track did not develop. A persistent pattern of subtropical easterly and mid-high latitude westerly flow anomalies may have intervened. Date line convection is now weakening; a portion is shifting southeast into the southern hemisphere and another is shifting west toward the west Pacific. Combined with eastward shifting convective activity over the Indian Ocean, a consolidation of positive convection anomalies around Indonesia has already occurred. This activity may eventually spread over the warmest SSTs currently in the west Pacific, south of the equator.

The current short term amplification and retrogression of the circulation anomalies over the Pacific Ocean will dominate the weather patterns during the next 1-2 weeks. Prospects do not look good for rain along the west coast during this time. The behavior of the circulation beyond week 2 is partially linked with the strength and location of tropical forcing. The Indian Ocean SSTs continue quite warm and we expect convection to redevelop there, possibly aided by a dynamical component from the recent MJO. Convection should also stay active over the west Pacific. If the west Pacific convection dominates (~GSDM Stage 2), a very boring weather pattern may be in the offing for the USA west coast beyond week 2. Increased activity over the Indian Ocean would lead to a better chance for a trough along the west coast and more favorable prospects for the American River Basin (ARB) (~GSDM Stage 4-1).

Please see our January 23rd posting for our weeks 1-3 outlook for the rest of the USA (CONUS). The cold regime scenario along with the precipitation concerns expressed in that discussion remain unchanged. Most models and their ensembles have come into good general agreement through at least days 7-10. We will try to do another posting early next week.

Klaus Weickmann and Ed Berry

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