Friday, May 27, 2011
"Songda" ramps up to super typhoon strength
Typhoon Songda in the northwest Pacific has ramped up wind speeds to a destructive 140 knots/hr (260 km/hr) gusting to 170 knots/hr (315 km/r) even as it skirted land and re-curved off Philippines and looked to spare Taiwan also.
The super typhoon of class-topping Category-5 strength on the Saffir-Simpson scale of storm intensity is expected to pause for some breath and decelerate as it emerges back into the northwest Pacific.
Expected to undergo weakening from Friday, Songda will have been reduced to a minimal cyclone by the time it rushes past Japan to the south and weakens further in the central Pacific.
The pull exerted by Songda on tropical moisture along the equator saw further convergence of monsoon clouds over the south Arabian Sea and adjoining equatorial Indian Ocean past Maldives and even approaching Sri Lanka.
Meanwhile, global models continued to maintain a watch for the formation of a weather system in the southeast Arabian Sea close to the Kerala coast during the first 10 days of June.
Some of these models also hinted the possibility of concurrent activity near the Oman coast during this period but without significant collateral damage to the monsoonal system.
In fact, the Climate Prediction Centre (CPC) of the US National Weather Services in its latest outlook valid for May 25 to 31 pointed to a band of enhanced convection and rainfall extending from south Arabian Sea towards equatorial Indian Ocean and Sri Lanka.
This is likely the handiwork of a Madden-Julian Oscillation (MJO) wave, a periodical upper air low-pressure wave, with direct impact on ground level weather and mostly associated with monsoon onsets.
The eastward propagating wave is seen as crossing into the Bay of Bengal during June 1 to 7 and entering South China Sea and the Maritime Continent (Indonesia, Malaysia etc), which is just as it should.
Global Forecasting System model of the CPC has hinted about the possibility of convective activity peaking to a high in south and southeast Arabian Sea during June 2 to 8.
Meanwhile, India Meteorological Department (IMD) has reduced the countdown for onset of southwest monsoon over South Andaman Sea to two days.
Satellite pictures on Thursday afternoon showed convective (rain-bearing) clouds rising over parts of Jammu and Kashmir, Haryana, northeast Rajasthan, Bihar, Jharkhand, Gangetic West Bengal, Orissa, Madhya Maharashtra, south peninsular India, east and south Bay of Bengal, Andaman Sea and south Arabian Sea
Monsoon Advances into Maldives, Sri Lanka and S, Central Andaman
Taken from http://rajesh26.blogspot.com/Monsoon Advances into Maldives Region and Sri Lankan Western and Southern Areas, and Central Andamans .
The Southern and Central Andamans are receiving sporadic rains for the last 3 days. Port Blair has measured 71 mms, 57 mms rainfall for the last 2 days, i.e. 25th/26th May. Port Blair got 114 mms in the 24 hrs ended 5.30 pm on Thursday.
As on 26th May, Vagaries advances the SWM as a weak current into the regions of Maldives , Sri Lanka and up to Central Andamans .
Heavy rains lashed Colombo on Thursday morning.
Vagaries is following and adopting the norms set by IMD for Monsoon Advance. All monsoon advances announced by Vagaries is as per the norms followed by IMD, but are strictly the veiws of the blogger, and for further commercial uses IMD may be referred to.
MONSOON ONSET NORMS OVER KERALA:
The guidelines are followed for declaring the onset of monsoon over Kerala.
1. RAINFALL
CRITERIA:- If after 10th May, 60% of the available 14 stations enlisted, viz. Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kasargode and Mangalore report rainfall of 2.5 mm or more for two consecutive days, the onset over Kerala be declared on the 2nd day, provided the following criteria are also in concurrence.
2. WIND FIELD
CRITERIA:- Depth of westerlies should be maintained upto 600 hPa, in the box equator to Lat. 10ºN and Long. 55 ºE to 80ºE. The zonal wind speed over the area bounded by Lat. 5-10ºN, Long. 70-80ºE should be of the order of 15 ? 20 Kts. at 925 hPa. The source of data can be RSMC wind analysis/satellite derived winds.
3. OUTGOING LONGWAVE RADIATION (OLR)
CRITERIA:- INSAT derived OLR value should be below 200 wm-2 in the box confined by Lat. 5-10ºN and Long. 70- 75ºE.
Northern Limit of Monsoon (NLM)
Southwest monsoon normally sets in over Kerala around 1st June. It advances northwards, usually in surges, and covers the entire country around 15th July. The NLM is the northern most limit of monsoon upto which it has advanced on any given day.
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