Tropical Cyclone Seven

[Cookie]

new system

http://www.wunderground.com/tropical/

Storm Alert issued at 4 Dec, 2008 6:00 GMT

Tropical Depression SEVEN is forecast to strike land to the following likelihood(s) at the given lead time(s):

Yellow Alert Country(s) or Province(s)

Sri Lanka

probability for CAT 1 or above is 10% in about 48 hours

probability for TS is 45% in about 48 hours

Yellow Alert City(s) and Town(s)

Batticaloa (7.7 N, 81.7 E)

probability for CAT 1 or above is 10% in about 48 hours

probability for TS is 45% in about 48 hours

Green Alert City(s) and Town(s)

Trincomalee (8.6 N, 81.2 E)

probability for TS is 40% in about 72 hours

Note that

Yellow Alert (Elevated) is CAT 1 or above to between 10% and 30% probability, or TS to above 50% probability.

Green Alert (Low) is TS to between 31% and 50% probability.

CAT 1 means Severe Cyclonic Storm strength winds of at least 74 mph, 119 km/h or 64 knots 1-min sustained.

TS means Tropical Storm strength winds of at least 39 mph, 63 km/h or 34 knots 1-min sustained.

[Somerset Squall]

Indeed, the very active end to the North Indian Cyclone season continues with the formation of the seventh tropical cyclone of the year. Intensity is currently 30kts and 07B consists of a well defined LLC with flaring (but not yet persistant) convection. 07B is forecast to move westwards along the southern periphery of a subtropical steering ridge to the north which is currently looking like persisting for the next day or so, which could make Sri Lanka a target for 07B. Favourable conditions of low to moderate shear and good outflow should promote intensification. JTWC are currently forecasting a peak of 50kts prior to landfall in Sri Lanka.

[Somerset Squall]

Shear has been stronger than anticipated over 07B and therefore the cyclone hasn't strengthened and intensity remains at 30kts. Convection has decreased a lot today and what remains is sheared west of the LLC. However, as 07B continues westwards it will move into a region of lower shear and thus a little modest strengthening is still forecast. 07B has jogged to the north through the day and this has had implications on future track. 07B is now likely to scrape the north coast of Sri Lanka and landfall as a stronger storm in India (due to decreased land interaction with Sri Lanka). This also means the southern half of Sri Lanka could remain largely unscathed. Still needs watching as the track is obviously not set in stone.

[Cookie]

thanks for the updates mate

[Somerset Squall]

07B has intensified overnight and intensity is now at 35kts. Convection is now attempting to wrap back around into the eastern quadrant of the storm but the LLC still remains partially exposed. Shear has eased over the storm, and outflow remains good, which has allowed the convection to increase and the cyclone to strengthen a little. Further intensification is possible as shear eases more, and 07B may make landfall in Sri Lanka at around 40-45kts. 07B has wobbled a little southwestwards again, and this creates more uncertainty just where 07B exactly will make landfall; predictions are a lot further south again after the wobble so it's pointless to speculate exactly where landfall will occur but Sri Lanka and Southern India will get a soaking from 07B, which of course isn't needed after the devestating TC Nisha a week or so back.

Edited December 6, 2008 by Somerset Squall

[Somerset Squall]

It appears that the southwest motion this morning was not a wobble, as 07B has continued to move west-southwest throughout the day. This now means that Sri Lanka will receive a direct landfall. Intensity is still at 35kts at the moment, but as 07B is fairly weak, tracking over Sri Lanka will probably dissipate the storm. The LLC is still well defined but convection is limited to a weak band to the west of the centre. If 07B survives interaction with Sri Lanka, the continued west-southwest track will take it to the south of India, and avoid further land interaction. It is therefore unlikely but more possible than earlier that 07B may move into the Arabian Sea next week. The tracking chart you posted Cookie shows the change in track and the anticipated miss of mainland India.

[Cookie]

the track hasn't half moved!

[Somerset Squall]

the track hasn't half moved!

Indeed!

07B has been declared a remnant low this morning, as there just has not been enough persistant convection near the centre for the last 6 hours. Sri Lanka may well finish off the LLC, but there is a small chance of regeneration if it survives. However, more than likely the remnants will be too weak to re-organise.

Edited December 7, 2008 by Somerset Squall

[Somerset Squall]

The remnant low of 07B is emerging to the west of Sri Lanka. Convection has increased a little this evening, and 07B is moving into a region of warm waters:

and lower shear (dark blue means low shear, bright red/white means high shear, the remnants of 07B are indicated with the letter 'L'):

The question is however, is there enough of a LLC to repsond to the favourable conditions. I'm having a hard time finding a discernable centre so it's still quite unlikely (but not impossible) for re-development to occur.

Sources:

http://www.wunderground.com/tropical/

http://cimss.ssec.wisc.edu/tropic/tropic.html

Edited December 7, 2008 by Somerset Squall

[Somerset Squall]

Convection is currently exploding around the remnant low of 07B this evening, though there is little evidence of formative banding features as yet. The improved satellite appearance however has prompted JTWC to flag up the chance of redevlopment. There is certainly some very deep, concentrated convection to the south of India around the weak low, this may help the low intensify. Chances for re-development into a tropical cyclone are increasing IMO. The image below shows this clearly (near the centre):

Edited December 8, 2008 by Somerset Squall

[Cookie]

this little one aint givening up!