Tuesday, December 20, 2011

The latest active phase cyclones

Tropical storm Washi formed around December 13, in the West Pacific (6N, 145E). At this point the MJO amplitude was weak. About a week earlier, though, the MJO had been quite strong - around 2 on the RMM scale - somewhere on the boundary between phase 4 and 5, which means active phase near the region of Washi's formation. This is pretty typical. The active MJO phase creates an environment favorable for tropical cyclone formation, but it often takes a few days or a week for the cyclones to actually get going. So the peak of cyclogenesis is not in the midst of the active phase, but a little later. It's fair to say that Washi probably owed its existence in part to the MJO.

Washi went on to do horrible damage on the island of Mindanao in the Philippines. The death toll now stands just below 1000. This is more than half the number of people who died in Hurricane Katrina. Yet this is not a story featured prominently in the news, at least here in the US.

In the meantime, at least some of the models are predicting a cyclone off the Top End of Australia, not far from the city of Darwin, in the next few days. Here's the GFS model's prediction of wind and relative humidity at 850 hPa (lower troposphere) for Christmas Eve:
The Australians living in this part of the Northern Territory have some experience with cyclones forming on Christmas Eve.

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