Really strange weather in Northern Australia (pictures)

There appears to be a tropical cyclone developing in Australia's north. This is not normally unusual - this is, after all, the time of year that cyclones develop in that part of the world. What is unusual is that the cyclone appears to be developing over land. More than that, it appears to be developing over an area that is not exactly known for its wetness - Australia's semi-arid north. In the BOM satellite pic below, you can clearly see a massive swirling cloud around 20° S 130° E. The swirling cloud is moving in a clockwise direction, which, in the southern hemisphere, is indicative of a low pressure system.




A just-released BOM synoptic chart shows that the low pressure system is a whoppingly low 955 hPa. And look to the East, there we see Tropical Cyclone "Jim" heading east towards the Solomon Islands. Notice what pressure that system is - 975 hPa. This means that the low centred over Australia's north is a more intense low than the cyclone to the north-east. They haven't called the low a cyclone yet - but for all intents and purposes there is one there!



I keep a daily eye on the ENSO figures these days, and things are looking good for a La Nina event. As the following graph shows, there is a sea temperature difference between Darwin and Tahiti of around +13 degrees. This means that, historically, Australia's north should produce more low pressure systems and cyclones and cause a lot more rainfall. Moreover, in the winter months, a positive ENSO result (indicating La Nina) means that there is a greater chance that these low pressure systems will continue, and bring a wetter winter to Australia's East Coast. La Nina is the opposite of El Nino, whereby low pressure systems are harder to develop because the water is cooler in Australia's north... and causes droughts in Eastern Australia. I'm sort of guessing that the land-based cyclone developing in Australia's north is a result of an increasing La Nina effect.



Here's the BOM weather warnings:

IDD20510
Australian Government Bureau of Meteorology
Northern Territory
Darwin Regional Forecasting Centre

FLOOD THREAT ADVICE
Issued by the BUREAU OF METEOROLOGY, DARWIN
at 1024 CST Sunday 29 JANUARY 2006

AREA INVOLVED
North of the Alice Springs District.

RAINFALL SUMMARY
Widespread falls of 10-20mm north of the Alice Springs district with lighter
falls across the northeast Top End. Heavier falls 40-80mm over the far southern
central Top End, eastern Victoria River District and into the western Barkly.
Isolated falls to near 100mm.

WEATHER SUMMARY
A deep monsoon low lies over the eastern Victoria River District near Elliott
and has recently moved a little to the southwest. The monsoon trough extends
from the low and across the Barkly and these features are the main focus for
rainfall, particularly the low. The low is expected to remain slow moving until
at least Tuesday.

FORECAST for the rest of today and Monday
Widespread falls 15-20mm and scattered moderate falls 20-50mm. Isolated heavy
falls of 60-80mm in the far southern Top End, western Barkly and Victoria River
District may lead to significant stream rises and flooding of low lying areas
while other falls may cause localised flooding and significant stream rises.

OUTLOOK for Tuesday and Wednesday
Widespread falls of 10-20mm, though less frequent about the northern Top End.
The active slow moving monsoon trough and low are expected to lie across central
parts of the NT between Katherine and Tennant Creek. The heavier falls about the
low will be of about 60-80mm while scattered falls of 40-60mm falls will
continue in the Victoria River District and across the Barkly and Roper-McArthur
Districts. The movement of the low from Tuesday is difficult to predict, but the
Victoria River District is still likely to receive some heavy falls with a
possible trend to increasing falls in the southern Victoria River and
northwestern Alice Springs District if the low drifts southwards. These falls
may lead to localised flooding and significant stream rises.

NEXT ADVICE
Around 11 am Monday

DARWIN Regional Forecasting Centre.