TROPICAL SYSTEM FORMATION (REVISED)

DATE: 16TH DECEMBER 2021 | TIME: 3:00PM BST (+6 GMT)
SUB: TROPICAL DEVELOPMENT | PERIOD: 18-21 DECEMBER 2021

(A) Under the influence of an Upper Air Circulation, a Low Pressure Area could form over Southwest adjoining South East Bay of Bengal by 17-18 December 2021.
It could intensify into a Well Marked LPA & then into a Tropical Depression (≥45kph) between 18-21 December over SE Bay of Bengal. Then it could be more marked by moving ENE/Eastward.
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▪️Overall confidence in the forecast has become moderate as the Disturbance remains disorganized & persists over South West adjoining SE Bay of Bengal & neighborhood.
So the expected intensification will be slow but delayed.
MJO signal found between Phase 6-7 with nearly Robust Amplitude(≤2) & it is likely to interfere destructively with low frequency La Nina base state over West Pacific & weaken subsequently.
Which is not supportive for Tropical development over Bay of Bengal.
While, Sea Surface Temperature is favourable(28-30°C) over most parts of Southern Bay of Bengal, which is conductive for the development process.
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Wind shear is currently low to moderate (⬇️) over the development area & decent outflow aloft along with potentially favourable parameters. But this combination is likely to depart for a while during middle of forecast  period as shear could increase then.
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That’s why, we have downgraded the probability into moderate value to intensify into a Depression.
•Max intensity is dependent on the track & future condition of the Bay of Bengal which is skeptical right now.
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Thus, The disturbance, Low to moderate VWS, Outflow & other favourable parameters are leading Moderate confidence in this forecast.
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(B) A pulse/disturbance could emerge into southern Andaman sea by 18/19 dec.
Due to High shear, it might not intensify.
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★See the Graphic to see visually the development areas & rainfall activity associated with the system track.
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◾ LANDFALL & MAX INTENSITY:-
Landfall Probability is skeptical right now & there is a possibility of dissipation over open water of South Andaman Sea.
If not, then it might cross southern Thailand by 22nd December as a weakening System.
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•The forecast track is based on the present data analysis & may not remain consistent if any change appears in the future data.
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Max intensity is skeptical right now & anticipated with the track & future condition of the Bay of Bengal.
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⚠️Effects:-
As the system will drift away from Sri Lanka, Rainfall probability associated with the system has withdrawn from Sri Lanka.
Andaman island, Sumatra, Southern Thailand &  Malaysia could have heavy to very heavy rain between 17-22nd December 2021.
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★Note:-
These informations are based on Present conditions & it might be changed somewhere during the entire forecast period.
So, keep eye on the latest update for better information.
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Stay connected, Stay alert, Stay Safe.
Thanks, ©BWOT
Bangladesh Weather Observation Team.