Wednesday, August 11, 2010

The IMD 925 wind map shows that the westerly flows have started into north-west India by replacing the easterlies in connection with a ‘break monsoon' condition, weakening trend in rainfall.

Break monsoon condition occurs when the monsoon trough shifts from its normal position over central India, northwards towards the foot of the Himalayas. During a break monsoon, heavy rain is to be expected along the Himalayan foothills and Northeast India, as the eastern end of the axis moves into theat region. "

Under the influence of an upper air cyclonic circulation, a feeble low pressure area is likely to form over northwest and adjoining westcentral Bay of Bengal today".- IMD bulletin today. This is also seen in the 925 wind map.
As discussed in yesterday's blog, this low would travel along the axis, and merge into it. As it moves, region around Delhi and western U.P. plauns can expect heavy rains around this weekend. An extended forecast for this week would be rainfall with heavy falls over the Western Himalayan region. Resultantly,with heavy rains in the catchments of some rivers, we may witness some rivers overflowing into the Bihar plains from Sunday.

Along with this break monsoon, the days have started getting warmer, rather hotter. Yesterday's highs, as seen in this map, shows a 40c (Hissar), a 39c, (Ganganagar), and several 36s and 37s in the north.
Several places in the south have also started seeing higher day temperatures, with pockets recording 37c. As discussed in the "vagaries" on 9th. I would estimate Bangalore to cross 31c.

These hot conditions with moisture conditions would facilitate building up of thunder cells and thunder showers in the interiors of Gujarat/Maharashtra/Karnataka. These would be restricted, initially, meaning on Wednesday/Thursday, to interior Gujarat, and then thundershowers would pop up in interior Maharshtra and Karnataka from Saturday.However,thunder cells would not be widespread, and would be in pockets.

Mumbai: With the sun shining, the days have started getting to 32c. Likely to continue with such weather. With a daily average rain of less than 10 mms, till Sunday, one may tend to think the monsoon is over. But a shower to two will be a reminder that the rainy season is not over. Chances of a thunder cell drifting over Mumbai on Sunday from the east. But will not attempt to confirm that !

International: From Mark's blog:
Hottest regions of U.S. Southwest "Whilst a return to 100-105 for both Vegas and Phoenix and perhaps a 115 at Death Valley, the cool, dreary coastl pattern continues with highs merely topping 60, Both San Diego and San Francisco will once again FAIL TO TOP 70, whilst LA should warm nicely to near 80 with PM sunshine. Look for midmorning clearing of clouds in the coastal Valley and highs topping the mid-80s, Palm Springs will likely warm towards 107-110 today. Lows tonight cool to the low 50s at the coast, 58-62 for the downtowns, 70s for the deserts, low 80s for Vegas and Phoenix".

With the abnormal heat centered right over Moscow airspace with a stunning 23 days above 90 degrees and even a couple of unprecidented 100s, I wonder whether in reaction within the atmosphere to a high pressure cell comparable or equivalent to that of the Middle East desert region forced so far north over Russia a direct response to the catastrophic flooding over Pakistan as the jet is shoved north and therefore either side of this, those troughs are enhancing the unsettled weather. To the west of the ridge there's been flooding over central Europe and an almost unbroken spell of unsettled and cool weather from Britain to Germany, to the east of the ridge, the jet has travelled so far south, it's crossing directly over Pakistan, driving abnormally cool air so far south and being meet by both tropical heat, humidity and of course very warm water, therefore is the jet's unusually far south positioned, caused by Russia's abnormally far north jet the reason for the "super monsoon"? Extra energy caused by the jet. We also must look at China also, which has seen the jertoverhead, enhancing thunderstorms, growing bigger storms and heavier, flooding rains. I believe the ridge over Russia is part responsible. As for the USA, we're seeing persistent heat and an unusually persistent heatwave centered between Dallas and DC (ironically the same areas which experienced the worst of the US winter last year). That high (like over Europe) has seen knock-on effects surrounding it with a persistent trough over the West Coast, producing an abnormally cool Coastal California summer and an extremely wet and stormy summer for the Northern Plains (similar to Pakistan, India and China), only it's not the monsoon? Where there's extreme heat, there's extreme rains downstream, we've even seen torrential downpours here across Scotland as warmth tries to push north, whilst cool air remains overtop, a nice set-up some thunderstorms. Today I could hardly see in front of me with the rain, water lay 1-2" deep on the highway and I even saw a shelf cloud, after a drove through a "storm" and eventually had to flip me "visor" down with the sun....


Anonymous said...

With the IMD announcing of an low around Vidarbha / S Chattisgarh today, what is the forecast for Mumbai? Does it change much as compared to what you had given on Wednesday?

Also, it appears (again as per IMD) that the Monsoon trough is going to shift North. Will this herald a 'Break Monsoon' condition as you had mentioned?

Rajesh said...

I have tried to answer your queries in the latest write up. Break monsoon was "short & sweet". Please go thru the blog, and let me know.