Thursday, May 15, 2008

Monsoon Watch-14

Bay Region: Today, I was most surprised to get a message from Vinson( Business Line) to check on the JTWC site. They had mentioned the likely formation of a cyclone in the bay. I always felt that this is not a probability now. As discussed in my earlier blogs, that this low will eventually "rain off" in the north bay area within a few days. For it to remain weak, there are several reasons:-1. low convection around it. 2.back to back W.D.s,causing dry north-westerlies to push it away. 3. very much near/on the coast. 4. Bay sst not warm enough for the system to turn into anything beyond a depression at the most.
Check the bay sst anomaly above, they are still at least 1.5-2c below normal in most of the bay.

The streamline map above shows the winds weakening a bit in the central bay. The formation of a tropical storm in the south china sea in the next few days will pull the main south westerly flow of the south andaman sea towards it. Hence, I still feel, that the monsoon will advance in the bay , by the 20th. The further advance into the north-eastern states will commence only after the formation of a trough from Assam to the central bay region, say by the 25th.

Arabian Sea: Read todays forecast given by the IMD. The monsoon , according to them will advance into Kerala between the 25th.May and 2nd. June ! Leaves nothing to imagination !
If we compare the sst anomaly map above and the sst anomaly map of the same time last year( shown below), we see the Arabian Sea is much cooler this year, if the same normal temperature is taken into consideration. Last year the warming trend at this time was more, and this year the same region is cooler.
However, the somali winds as seen in the streamline map, are picking up, and a distinct cooling(yellow) off the somali coast is now seen. I feel, the sst of the Arabian Sea vis-a-vis the somali current and otherwise will be geared up for monsoon clouds to start forming in the sea off the Kerala coast from the 25th. Another 4/5 days thence, and the monsoon can touch Kerala.

Sub Continent: The jig-saw puzzle of the monsoon can fit in properly in the bay and Arabian sea, but I only hope the sub continent heating and seasonal low formation in the north do not play spoilsport. The heating even today(wednessday) is mediocre, with the highest in Pakistan today( 14th) at 47c, Nawabshah,and with only a stray 44c at Nagpur and Vijaywada in India. The heat low just about touched 998mb in a small area on the 14th. A difference of atleast 16mb in the pressure is required between the MSL at Trivandrum and the pressure in the heat low to create a gradiant to pull the monsoon winds and clouds inland.


Mani said...

Hi Rajesh, I checked out this website and SST anomaly is not that on the Arabian sea side. So don't know which one to believe IRI or FNMOC.

Btw in the bay between Mexico and Florida they say when the temperatures are about 28-29, thats good enough for tropical storms. Why Arabian sea and Bay needs to be near around 31 for monsoon to start?

Mani said...

The website I was saying was the FMNOC website.