Saturday, December 24, 2011

On a long-lived MJO event, and another Sri Lankan cyclone

We really seem right back in an active MJO phase in the Indian ocean.  Is it a new MJO event or did the old one never really leave as it was supposed to?  This comes down to a matter of what the MJO really is.  If it's something that goes eastward at a certain phase speed, then this is a new event.  But if we allow a little more flexibility - if we had a definition in terms of MJO dynamics rather than just statistical properties - then it's not so clear.  Maybe some MJO events just don't do so well at the propagating eastward part.

In any case, the satellite images from the water vapor IR channel of Meteosat as well as the MIMIC total column water vapor product both show the jellyfish structure, with the head of the jellyfish pushing up against Sumatra from the west:

The jellyfish is often a precursor to the formation of tropical cyclones.  Indeed the northern blob of clouds just east of Sri Lanka has been declared an "invest" by the JTWC.  Their current statement on the system says that the potential for the development of a significant tropical cyclone is "medium".  After my earlier experience, I now pay close attention to what happens here.  The Sri Lanka Meteorological Department does, to their credit, have a bad weather warning out on this system.  They politely say that "the fishing and naval community are kindly advised to refrain from their activities" in the region of the storm.  They do not, however, make any mention of the fact that there is a significant probability of this system becoming a proper tropical cyclone.  They have a specific area of their web page for cyclone warnings, which is currently blank.

As usual our information about what will happen in the future is in part based on numerical models.  Here is the 24-hour forecast of low-level (850 hPa) wind and relative humidity from the NOAA GFS model, valid 12Z Christmas day.  Note the swirling winds just east of Sri Lanka:
Also note the consistency with the GFS run of a few days ago shown in the previous post (valid the preceding day, today).  I didn't talk about this Sri Lankan system in that post but it was there in the model.  The consistency from run to run does remind me of the November storm.

I don't understand why the Sri Lankan forecasters (and as far as I can tell, the Indian ones as well - the IMD has no cyclone warning that I can find on this system either) think it would be so wrong to tell the public that there is a good chance a cyclone might form soon.  Surely they know that the potential is there;  they just seem not to want to use the word "cyclone" until one actually exists.  But that word gets people's attention more than just "bad weather" does, and is more likely to change people's actions.  Yes, there is a chance of over-warning, but isn't it better to take that risk if it could save lives?

Astute observers will notice that the GFS model is also still spinning up the sytem off the top end of Australia.  That system is not impressive yet, but JTWC statement on it rates its potential for becoming a significant cyclone within the next 24 hours as "high".  The Australian Bureau of Meteorology's forecast is here.  It isn't forecast to hit Darwin at this point, but still, the timing is spooky, for those who know Darwin's history with tropical cyclones.

1 comment:

  1. I like the description of the pattern as a "jellyfish." I've never thought about that before, but it really is fitting.