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Darwin tropical diagnostic statement



Darwin tropical diagnostic statement

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Darwin Regional Specialised Meteorological Centre


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Cyclones -- Australia -- Periodicals; Cyclones -- Northern Territory -- Periodicals

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Bureau of Meteorology, Northern Territory Region

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moved west northwest and became a typhoon on the 30th. It crossed the northern Philippines on the 2nd December and entered the South China Sea. After making landfall the system weakened and began recurvature on the 3rd of December, moving initially to the north and then to the northeast. On the 4th of December it just touched the southern tip of Taiwan and merged in a frontal system while undergoing transition to an extra tropical system. Media reports indicate several people were evacuated in the northern Philippines to reduce the loss of life after a tropical depression had caused extensive loss of life and property damage just before the approach of the typhoon. SEA SURFACE TEMPERATURE [Figs. 3a, 3b] Warm SST anomalies between +0.5 and +1.0C dominated large areas within the equatorial oceans. The west Pacific warm pool remained focussed near the date line, though warm anomalies extended both eastwards and westwards during November. The large pool of warm sub-surface waters in the central Pacific that has been evident for several months persisted during November (outside of map coverage). This was considered consistent with a shift towards El Nio, though was not followed by other typical El Nio trends. For instance, the SSTs of the east Pacific cool tongue close to the South American coast (not shown on the map) persisted during November (though showed some warming trends during the month). The northern Indian Ocean remained mostly warmer than normal. MSL PRESSURE [Figs. 4a, 4b] Above average mean sea level pressures prevailed over most of the equatorial western Pacific and maritime continent except for a few equatorial areas close to the date line. Most of the tropical Indian Ocean experienced pressures lower than climatology. Below average pressures in the southern Indian Ocean were consistent with the formation of two tropical cyclones in the region during the month. 850 hPa FLOW [Figs. 5a, 5b] Near-equatorial troughs on either side of the equator persisted during most of November. The tropical circulation was mostly close to climatology. The passage of long waves in the subtropical highpressure system made the flow more meridional in each hemisphere and contributed to the stronger than normal easterly flow over northern Australia. The wind anomalies near the date line in the equatorial Pacific indicate near normal conditions in the area. 200 hPa FLOW [Figs 6a, 6b] Slightly above normal easterly flow prevailed in the equatorial Pacific close to the date line. The easterly flow over equatorial Indian Ocean remained weaker than normal. In the extratropical regions, the STRs were dominated by propagating long waves giving rise to a more meridional flow than climatology. VELOCITY POTENTIAL [Figs 7a, 7b] Velocity potential, which is a proxy for convergence, indicates a good vertical alignment of low-level convergence and upper level divergence associated with the near equatorial troughs and the SPCZ 3