Possible NT cyclone for Xmas Day

An intensifying tropical low just over 200km north of Darwin off the Top End coast is expected to develop into a tropical cyclone early on Christmas Day. If it forms, it will be named Grant. A Cyclone Watch is current for coastal areas from Dundee Beach to Nhulunbuy, including Darwin.

While models are uncertain about the intensity and movement of this system, heavy rain is predicted for the north coast of the NT due to its slow-moving nature and proximity to the coast. Over 400mm is possible over the next few days with flooding likely.

If this tropical low develops into a tropical cyclone, it will be the third in the Australian region so far this season. Earlier in the month, Cyclone Alenga (named by Mauritius) drifted into the Australian Region of Responsibility but dissipated well off the coast with no impact on the west coast. The second of the season was a very shortlived Cyclone Fina in the Coral Sea, several hundreds of kiometres off the QLD coast.While this system had no direct impact on the coast, it is going to have a major influence on coastal conditions in southern QLD over the Christmas weekend. Cyclonic swell will coincide with a King Tide to produce waves of 8-10 foot extending to parts of northern NSW aswell. This will be a very dangerous time for holiday-makers wanting to go swimming, surfing and rock fishing, and there is a threat of beach erosion and inundation of low-lying areas.

Severe weather is also expected for south-eastern Australia during the Christmas period with a major thunderstorm outbreak! A hot, humid airmass is combining with a deepening trough to trigger widespread thunderstorms in TAS, VIC, southern NSW and the ACT on Christmas Day (including Melbourne and Canberra), moving north through central and northern NSW (including Sydney) on Boxing Day. Damaging winds, flash flooding and large hail are all possible!

Severe storms strike Perth with record breaking December rain!

Severe thunderstorms struck much of WA's southwest last night leading to widespread local flooding. Perth was soaked by a massive 44mm, with 37.8mm falling in just 46 minutes- this was greater than a 1 in 100 year event and, the equivalent of 3 times the December monthly average rainfall in just 46 minutes! It was also Perth's wettest December daily rainfall total in 60 years!

Surrounding areas were also awash with heavy rainfall Mandurah 69mm (heaviest December rain on record), Serpentine 37mm, Rottnest Island 36, Perth Airport 35 and Swanbourne 30mm.

The worst affected region was the Great Southern district with a large number of towns recording their heaviest December rainfall on record including: Narrogin (84.4mm), Wishbone (81.6mm), Dumbleyung (71mm), Rushy Pool (70mm), Katanning (61.8mm) and many others.

Williams had the highest rainfall in this event with a massive 125.6mm- the highest rain total ever recorded anywhere in the South West Land Division in December! This resulted in widespread flooding leading to evacuations.

The low pressure system responsible for the heavy rain and severe thunderstorms is moving eastwards today so rain has already eased for the west coast. Since 9am this morning, another 20-40mm has already been recorded in parts of the Wheatbelt, Goldfields and Southeast Coastal districts. As the system reaches the SA border it is expected to weaken, bringing patchy light rain to that state.

Widespread cloud cover due to rain and storms will capped maximums today with temperatures as much 13 below average for this time of year. Newdegate and Narrogin reached just 16 and 17 degrees today, respectively.

Summer is typically very dry for Perth with the city averaging only 12.8mm during December. This year has been very unusual for Perth and much of south-western WA with the city already receiving 75.8mm- now just 5mm short of its wettest December on record! 2011 marks a huge turnaround in rainfall from December 2010 when Perth recorded only 3.4mm.

First cyclone of the season in Australian waters likely to fizzle

Infared Image from Japan Meteorological Agency satellite MTSAT via Bureau of Meteorology- TC Alenga is the bright green/red system in the top left corner.

We could see the first tropical cyclone of the 2011-12 season in Australian waters with TC Alenga entering the Australian region of responsibility some time today.

It's situated in the central Indian Ocean and moving east southeast at 13kmh. It's expected to weaken on Thursday and Friday, and then dissipate well off the west coast of Australia due to unfavourable sea surface temperatures and atmospheric conditions. At this stage, the only influence that this system might have on the Australian mainland is rain for parts of the west coast like the Gascoyne/Pilbara due to increased moisture from the outflow of the cyclone.

I'll keep you posted!