20 replies to this topic

[Somerset Squall]

The fourth tropical depression of the seaon has formed just west of Luzon in the South China Sea. 04W's intensity is 30kts, and the depression is sat in a favourable environment for intensification. Deep convection has persisted over the increasingly well defined LLC, prompting the upgrade. Low shear, warm sea temperatures and strong poleward outflow should allow strengthening until landfall- JTWC forecast a peak of 60kts so there is a chance 04W will go higher and become the season's second typhoon.

04W is moving towards the northwest, and should turn towards the north-northwest as the ridging that steered Conson has been weakened significantly by the former typhoon. This puts Hong Kong in the firing line for landfall.

Edited by Somerset Squall, 18 July 2010 - 10:01 .

[cookie]

do you think that ridge will re-strengthen?

[Somerset Squall]

Difficult to say really, quite hard to predict as you saw from JTWC struggling with the track of Conson. What I will say however is that Conson was a large typhoon which has practically inilated the ridge- which therefore could take some time to reform.

[cookie]

another question again, will the waters be cooler over this area after Conson went through?

[Somerset Squall]

Although Conson has cooled the waters slightly, 04W will be tracking over waters to the north of where Conson went through, which are undisturbed and still very warm. With good poleward outflow and low shear, there is actually potential for some rapid intensification.

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[Somerset Squall]

As those images show Cookie, 04W is not very organised, and remains a depression. Land interaction with Luzon is probably playing a role in this. However, the depression has tracked westwards away from land so should now begin to consolidate further. A swing to the north-northwest is also still forecast as 04W gets steered along southwestern periphery of an elongated ridge extending from Taiwan to Japan. Landfall is still expected near Hong Kong but model spread is fairly wide, and the cone of uncertainty does extend as far west as Hainan Island.

[Somerset Squall]

04W has been ugraded to Tropical Storm Chanthu, with intensity rising to 35kts. Chanthu looks much better on satellite imagery than this morning, with more prominant banding features and more concentrated convection slowly contracting towards the centre. Once Chanthu manages to fill in the conective gap near the LLC, then proper intensification can begin. Shear is very low throughout the south China Sea, and waters are warm towards the north (where Chanthu is heading). Don't rule out this one becoming a typhoon even though it's not explicitly forecast.

Chanthu has turned towards the west-northwest over the last 6 hours, and should bend more towards the north-northwest through the day. Landfall is still quite hard to predict, with as far west as Hainan Island and as far east as Hong Kong being plausible.

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[Somerset Squall]

Chanthu has struggled over the last 9 hours. Convection is still pretty scarce near the LLC, and thus Chanthu remains a tropical storm of 35kt intensity. Looking at CIMSS shear maps, elevated shear is present in a wide swathe to the northwest of Chanthu, which the storm is on collision course for. (Look at the left side of the map in the South China Sea to see the 30-40kts of shear near Hainan Island):



This shear will arrive later today over Chanthu, and it is likely to hinder further strengthening of the storm. Because Chanthu is quite a large storm it may not feel the effects of the shear immediately, and I suppose it is for this reason that JTWC are still froecasting a 45kt peak of intensity before landfall, which is still expected to occur midway between Hainan and Hong Kong.

[Somerset Squall]

Shear is notoriously difficult to predict, and has not reached Chanthu thus far as was expected. In response, Chanthu has strengthened to 45kts. The storm is much better organised than earlier with good central convection which Chanthu has lacked so far. The trough responsable for the higher shear near Hainan Island has now moved further away, meaning Chanthu is now likely to continue intensifying up until landfall just west of Hong Kong.

[Somerset Squall]

Chanthu has intensified further overnight, with sustained winds rising to 55kts. Deep convective banding is wrapping healthily around the LLC which is still covered by a decent amount of convection. Landfall is expected to occur just beyond 24hrs, closer to Hainan Island than Hong Kong. Chanthu does have a small shot at typhoon status, though it's considered unlikely at this time.

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[cookie]

[Somerset Squall]

Looking at Cookie's image above, it appears an eye could be forming in the small central dense overcast. Intensity has increased to 60kts, so Chanthu is certainly on the verge of becoming the season's second typhoon. However, time in running out with landfall expected to occur between 12-18hrs. Certainly looks quite impressive at present.

[cookie]

Stunning image

[Somerset Squall]

Indeed it does Cookie, and Chanthu has now become a 65kt, cat 1 typhoon. Chanthu is less than 12hrs away from landfall, so any additional intensification will be limited.

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Quote

BLACK rainstorm warning now in effect here in Hong Kong. First time it's been issued since 2008, rainfall rates exceeding 70mm per hours. Chanthu really has got a sting in it's tail!

"Black Rainstorm Warning Signal Special Announcement issued by the Hong Kong Observatory at 5:30 p.m.

The Rainstorm Warning Signal is now Black. This means that heavy rain has fallen or is expected to fall generally over Hong Kong, exceeding 70 millimetres in an hour, and is likely to continue.

Because of seriously flooded roads and inclement weather conditions, you are advised to take shelter in a safe place and stay there. Parents, students, school authorities and school-bus drivers should listen to radio or television announcements on schools. Do not attempt to travel until the
Black Rainstorm Warning Signal is no longer in force and traffic conditions have improved.

Please listen to radio or watch television for traffic conditions and further announcements on the rainstorm.

Dispatched by Hong Kong Observatory at 17:30 HKT on 22.07.2010"

[cookie]

Looking very good this morning

[Somerset Squall]

Thanks for posting that one Cookie, shows that even though Chanthu is now making landfall closer to Hainan Island, it is important not to focus on the exact point of landfall.

Chanthu has developed a large eye as it crosses the coast, and intensity has increased to 75kts, making the typhoon joint strongest so far with Conson in terms of windspeed, though Chanthu is strongest overall as pressure has fallen to 965mb (apposed to Conson's 970mb). This last minute intensification does not bode well for Hainan Island and neighbouring areas which now have some much stronger winds to contend with than earlier thought. As Cookie's extract suggests above, some dangerous flooding rains are poised to spread in anywhere form Hainan Island to Hong Kong. As Chanthu degenerates inland, rains will also spread into northern Vietnam as Chanthu veers towards the west-northwest in the low level flow. The rains shouldn't be quite so severe here.

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