Tropical Highlights

  Table of Atmospheric Indices  (Table 1)

  Table of Oceanic Indices  (Table 2)

  Time Series

  Time-Longitude Sections

  Mean & Anomaly Fields

  Appendix 1: Outside Contributions

Tropical Highlights

AUGUST 2009

Sea surface temperature (SST) anomalies remained above average across the equatorial Pacific Ocean during August 2009 (Fig. T18).  Consequently, all of the Niño-region SST indices were between +0.8°C and +1.0°C throughout the month (Table T2, Fig. T5).

The oceanic thermocline along the equator, measured by the depth of the 20°C isotherm, remained deeper than average across the equatorial Pacific Ocean during August (Figs. T15, T16). Consistent with these conditions, temperatures were 1^o-3^oC above average at thermocline depth across the equatorial Pacific (Fig. T17).  Also during August, convection was suppressed across Indonesia and the western Pacific (Figs. T25, E3). The coupling of the oceanic and atmospheric anomalies indicates a weak El Niño.

The tropical circulation also featured intra-seasonal activity associated with the MJO (Fig. T12), which masked the El Niño-related pattern of enhanced convection over the central equatorial Pacific. The MJO also produced a westerly wind burst in the western tropical Pacific early in the month (Fig. T13), which triggered an eastward propagating oceanic Kelvin wave. This wave contributed to a deepening of the oceanic thermocline during the month, and to in increase in oceanic heat content in the central equatorial Pacific (Fig. T17). Previously, the upwelling phase of a Kelvin wave had led to a temporary weakening of the positive sub-surface temperature anomalies in the eastern Pacific.

Elsewhere, convection was enhanced over the eastern tropical Pacific during August, in association with a very active month of tropical cyclone activities in that region. Over the tropical Atlantic , the ITCZ was shifted north of normal, in association with an enhanced west African monsoon circulation (Fig. T24), weaker than average easterly trade winds in the deep tropics (Fig. T20), and a northward shift of the 700-hPa African easterly jet. These conditions contributed to the development of four Atlantic named storms (including Major Hurricane Bill), despite anomalous upper-level westerly winds (Fig. T21) and increased vertical wind shear over the Caribbean Sea in association with El Niño.

For the latest status of the ENSO cycle see the ENSO Diagnostic Discussion at:   

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html