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Somerset Squall

Tropical Storm Dujuan

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Invest 93W has become TD13W to the northeast of the Philippines, with an initial intensity of 25kts. The circulation, though still broad, is now closed and has some deep convection persisting in the vicinity. 13W is in a low shear, warm sea temperature environment which favours intensification over the next 4 days. However, strengthening will be slow at first due to the broad nature of the circulation. Nonetheless, JTWC forecast gradual intensification into a typhoon.

13W is in a weak steering environment at present and has not moved much whilst developing. However, a developing ridge to the south and east should force 13W northeastwards away from the Philippines. The only country likely to be affected by 13W is Japan, if it makes it that far.

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JMA have upgraded 13W to a 35kt tropical storm, named Dujuan. Dujuan still has a rather broad circulation with deep convection attempting to consolidate around this centre. However, at the present time, Dujuan is rather lopsided with most of the convection lumped to the south, displaced by moderate shear. With the broad LLC and moderate shear, strengthening is unlikely to be rapid. Waters will remain warm and in about 36hrs time Dujuan may move into a lower sheared environment which may facilitate more speedy intensification to typhoon status. Steering currents look identical to before so the track forecast has not changed.

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As expected, Dujuan has been slow to strengthen. Convection has continued to be sheared south of the broad LLC. However, over the last few hours the LLC has become better defined and has contracted. In addition, convection has become more concentrated over the centre and remains very deep. This is a sign that the shear is finally easing, and this should allow some faster intensification to occur. Intensity is currently at 45kts and Dujuan has a good chance of becoming a typhoon.

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Dujuan has failed to consolidate any further despite favourable conditions, and intensity has remained steady at 45kts over the last 48hrs. Dujuan's problem has been the broad LLC and weak inner structure, it just has not been able to tighten itself up at all. Dujuan is also a fairly large storm which hasn't helped. A similar thing happened to Typhoon Morakot- the conditions where there for that storm to become a cat 4 but because of the size and messy inner core the typhoon only peaked a cat 2. Dujuan is unlikely to become a typhoon now as shear will soon increase; in fact, shear is already high over the northern half of the LLC, preventing sustained convection here. Most of the remaining convection is located in a band to the south. With the brisk northeasterly heading, Dujuan will be moving over cooler waters aswell, which will induce extratropical transition by 48hrs and complete it by 72hrs. JMA show strengthening in this time frame, but this is likely to be as an extratropical storm. Dujuan may brush close to southeastern Japan but not as close as Tropical Storm Krovanh did last week.

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Dujuan weakened to a 30kt tropical depression this morning as convection failed to make a comeback over the LLC. The deep convection that remains in association with Dujuan is limited to a band to the southwest of the LLC. Shear is high and the waters increasingly cold so extratropical transition should begin within the next few hours. Once Dujuan becomes extratropical it has a chance to re-intensify into a powerful low in the open waters of the North Pacific.

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Convection has increased substantially over the LLC of Dujuan overnight, and the system has been re-upgraded to a tropical storm, with intensity of 40kts. However, strong shear and passage over colder waters should initiate extratropical transition very soon.

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Dujuan maintained the convection this morning and even showed signs of an eye. Dujuan's intensity has increased and is now at 55kts. Dujuan looked betyter than it ever did before this morning, funny really as the system was moving over cooler waters. Dujuan seems to be finally succumbing to the high sher and cold waters and looks to losing the warm core. ET is expected to be complete within 12hrs.

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Dujuan maintained the convection this morning and even showed signs of an eye. Dujuan's intensity has increased and is now at 55kts. Dujuan looked betyter than it ever did before this morning, funny really as the system was moving over cooler waters. Dujuan seems to be finally succumbing to the high sher and cold waters and looks to losing the warm core. ET is expected to be complete within 12hrs.

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must be over some really cold waters now

ZCZC 543

WTPQ20 RJTD 091500

RSMC TROPICAL CYCLONE ADVISORY

NAME STS 0912 DUJUAN (0912)

ANALYSIS

PSTN 091500UTC 38.1N 157.6E FAIR

MOVE NE 34KT

PRES 980HPA

MXWD 050KT

GUST 070KT

30KT 260NM

FORECAST

24HF 101500UTC 47.8N 172.8E 130NM 70% EXTRATROPICAL LOW =

NNNN

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