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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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4 region. The foci of implied vertical motion are located near the SPCZ and central Indian Ocean, rather than the maritime continent, implying a shift in the typical Walker circulation during the month. OUT-GOING LONG-WAVE RADIATION (OLR) [Figs 8a, 8b] The OLR anomaly pattern for the month of November more or less coincide with the pressure anomalies and velocity potential indicating more convective areas in the Indian Ocean, the SPCZ area and equatorial areas close to the date line. The above average convection in the northwestern Pacific matches with the areas of cyclone tracks in the region. Equatorial areas between 90E and 150E including Australia had less than average convection during the month. CROSS-EQUATORIAL INTERACTION [Fig. 9] The vertical cross-section of the meridional wind pattern across the equator is shown in figure 9. The cross equatorial flow pattern was close to normal at lower levels except near 80E where a stronger than normal southerly flow prevailed, mainly due to the convective activity that prevailed in the southern Bay of Bengal during the month. The flow was close to climatology in the upper levels. 850 hPa WIND COMPONENTS AT DARWIN [Figs. 10a, 10b] A stronger than average southeasterly flow prevailed over Darwin during most of November. A few heavy rainfall events contributed to a total monthly rainfall of 105.2 mm. The median and mean rainfalls for the month of November are 140.5 mm and 141.2 mm respectively. INTRA-SEASONAL VARIATIONS [Figs. 11,12,13] The first active phase of Madden-Julian Oscillation [MJO] during the northern hemisphere monsoon occurred over India and southeast Asia around late April to early May, extending to the northwest Pacific around the middle of May. The following active event impacted over much of south Asia around early June. A marked suppressed phase was then evident over Indian longitudes around the middle of June, extending eastwards to the northwest Pacific for the early part of July. The next active phase had its greatest influence on the Indian monsoon from the middle of July, extending eastward to the western Pacific for much of August. A weak MJO progressed across the Indian and the western Pacific from late August to early September. The stronger convection in the central Indian Ocean during late September was associated with another active MJO pulse and remained active over the SPCZ area during early October. The enhanced convection, which became apparent over the equatorial Indian Ocean during late October, was confined to the area for several weeks but waned as it approached the maritime continent, where convection in the near equatorial belt has been suppressed for the last couple of months. Another enhanced convection event appeared in the Indian Ocean during late November and convective activity soon after increased in the western Pacific, which may have been associated with a weak MJO event. Despite several active MJO events having progressed into the Pacific region in recent months they have not been a trigger for sustained active convection over the Pacific SST warm pool, which has been in place over the equatorial date line.