Tropical cyclone Sidr ( Bay of Bengal )

[Helge Tuschy]

A potential very dangerous cyclone is heading northwards. Sidr intensified quite rapidly over a 12h period yesterday and reached 115kt. Polar outflow was / is well established and it had a quite circular and compact looking central dense overcast. The outflow should stay well established as entrance region of an intense upper-level jet still points towards the system, but this is forecast to change as flow becomes slightly more zonal. Hence upper support could become at least somewhat less favorable but at the same time the system is forecast to cross an area with higher heat content ( SST anomaly of +2°C and more ... )over the nort-central Bay of Bengal which could offset the aforementioned slightly more negative aspect.
Mid-level flow becomes more intense, but I honestly see no real reason why shear should become that strong that weakening could be anticipated ( like the JTWC did ). Ok...CIMMs has quite a lot of shear but I'm not sure how much shear can be ignored as system starts to speed up .

Anyway... model pool finally initialized the current strength of this system and a significant shift towards the east was the result with a now more NNW / N track of this storm.
It looks increasingly likely that a strong or even intense cyclone will hit an area which had a comparable storm many years ago ( 1998/99 dependant which area will be hit ) and we talk about a potential heavily popluated area ( e.g. Calcutta 10-15 million ( agglomeration included ). This COULD be a very dangerous storm !

Sorry for the bad English.

Cheers, Helge

 

[Josh Morgerman]

Helge, your English is great.

Re: Sidr... The Joint Typhoon Warning Center's 18Z package puts initial intensity at 115 kt but forecasts rapid weakening over the next two days as the cyclone moves N, into a high-shear environment. The 48-hr position has the center approaching Calcutta, India, with winds of only 85 kt (Cat 2).

I also notice that the cyclone's satellite presentation has deteriorated since yesterday-- the eye is no longer distinct.

This setup reminds me of N-moving hurricanes landfalling along the N coast of the Gulf of Mexico. They often-- but not always-- weaken this way as they move N into a more hostile environment-- i.e., Opal 1995, Lili 2002, Ivan 2004, Dennis 2005, Katrina 2005, and Rita 2005, to name just a few recent examples.

 

[Stuart Robinson]

Ether way (Even if the storm does actually weaken before landfall) as significant surge will already be present.

Sadly this will swamp the Bangladesh Delta - an area that is ill prepaired to cope with this sort of Event.

 

[Josh Morgerman]

The JTWC's 00Z package brings the cyclone ashore very near the India-Bangladesh border-- just SE of Calcutta-- in ~48 hrs with winds of 70 kt (Cat 1). Strong upper-level winds N of 18N will take their toll.

 

[Helge Tuschy]

Hm...I'm not so sure if this intensity forecast will verify. The main player looks like to be a mid-level trough over eastern India. Winds at mid-levels really start to increase as the system approaches, but otherwise winds are not on a sign. increase. I'm not so familiar with situations where only the mid-level wind ramps up while the rest of the background-flow stays nearly the same...
I agree...SSTs are slightly cooler just sout of Bangladesh, but still warm enough. Upper-level winds over Bangladesh become more divergent and hence the support for the polar outflow should relax and the aformentined winds at 500hPa are on the increase. There are enough indications that a weakening trend can be anticipated but I'm not sure if it will weaken that much. RSMC ( India ) has a quite intense system coming onshore SE of Calcutta.

Sidr now came back to a T 6.0 and ( CIMMS has CI 6.5 ) and has a well structured core . Let's see how the storm evolves and how strong the shear finally will be. But I agree...even a strong tropical storm could have a very bad affect for those people.

 

[Josh Morgerman]

Helge, I was wondering the same thing this morning. After deteriotating a bit, the cyclone looks very healthy again. I also notice that the JTWC has increased the intensity forecast, putting it at 110 kt before landfall and 80 kt right after. Hmmm.

 

[Jonathan Whitehead]

Wow I actually saw this on TWC this morning in the NWC atrium. I had no idea. Its perfectly symmetric too.
Check out RAMSDIS
http://rammb.cira.colostate.edu/ram...at.asp?product=tropical_metio_4km_ir4_floater

 

[Josh Morgerman]

Helge, I'm starting to think you're right Re: this!

The cyclone is already at 17N and the satellite presentation is excellent-- with a clear, symmetrically-placed eye, a solid CDO, and no appreciable degradation. The Navy/NRL puts the intensity at a very severe 926 mb/130 kt.

Furthermore, if the JTWC forecast track verifies, it's a near-perfect placement of the right-front quad for funneling water up into the narrow top of the Bay of Bengal. It's textbook. As the cyclone should make landfall close to the India-Bangladesh border, India (to the left) should get off easier, but Bangladesh (to the right) will experience the highest surges.

I'm wondering if the JTWC might have significantly under-forecasted the landfall intensity. It will be interesting to see if their next package increases that.

 

[Josh Morgerman]

The new JTWC package is out, and their forecast is now alarmingly bullish: initial intensity is 130 kt, and they put the center near the coast-- at the India-Bangladesh border-- in ~24 hrs with winds of 115 kt (Cat 4). Wow.

On the latest microwave imagery, the inner core looks really solid-- and it appears to have contracted a bit.

 

[Jonathan Whitehead]

whats JTWC and where/how does one get this forecast?

how come a lot of the moisture/blowoff is going north? It appears theres a high pressure over SE Asia since the theres a clockwise rotation from Laos and Cambodia up into the typhoon.

 

[Josh Morgerman]

whats JTWC and where/how does one get this forecast?

JTWC = Joint Typhoon Warning Center, which is the U.S. government agency that issues warnings for tropical cyclones in other regions of the world outside of the N Atlantic (which is covered by the NHC).

Here's the JTWC site: https://metocph.nmci.navy.mil/jtwc.php

Enjoy!

 

[Josh Morgerman]

Re: Sidr... I just looked at some spectacular microwave imagery of this cyclone, showing a very tight, contracted eyewall, and some estimates now put the intensity at Cat 5!

Given how small the inner core is, and also the fact that it's moving into a less favorable environment, I expect there will be some fluctuation and/or reduction in the intensity prior to landfall in ~24 hours-- but this will be a serious storm when it blows ashore.

 

[Jonathan Whitehead]

I know this is an out of the way location newswise but does anyone have any pictures from area they can send. Like Im now really interested in whats going on there. I wish TWC would send one of their reporters over there to the coast, that would be awesome. Hell if CNN can do the same for Iraq, why not Calcutta?

 

[Helge Tuschy]

Latest numbers indicate a cat.5 cyclone with winds somehwhere between 135 and 140kt and a pressure around 900 hPa. I agree that this should be the best environment Sidr will have in his life time. From now on everything gets worse and one should not forget that this is a very small center ( latest remark even has the word pinhole in its bulletin ) and intensity fluctuations could be quite dramatic if the center gets more disorganized but this should be a quite compact and strong cyclone, coming onshore. Keeping in mind that this area had no real storm for years and how many poor people live in this area this could become a quite dramatic event. Let's hope that the shear takes its toll on the storm's intensity...otherwise this will be indeed a dramatic Cat.3 and above storm.

Helge

 

[Helge Tuschy]

In the last advisory Sidr became a catastrophic Kat.5 cyclone just south of Bangladesh. I have to admit that I do not really agree with the JTWC regarding the wind speeds. The cyclone was extremely well developed during the past 24 hours ( refering to microwave data ) and the main reason, why it was not increased was the pretty cold eye and hence low numbers ( 7.0 with ADT of 7.3 , and a big spread between 115kt and 145kt ). I think that Sidr was well above 130kt during the past 12-24 hours as it crossed the area with positive SST anomalies.
Now the microwave images hint on a detoriating LLCC and weakening eyewall structure ( maybe an eyewall replacement cycle )and I think the main reason for upgrading to a Cat. 5 was the warming trend of the eye during the past 6 hours ( only a few degrees ) , which supported an increase of the so called cira multiplatform sat intensity estimate to 129 KNOTS AT 150600Z ( referring JTWC ) ( so an increase of 7kt compared to the past hours and hence a decrease in spread of the numbers). But well...I'm just a meteorology student from Innsbruck ( Austria) and I do not have the knowledge of those people (JTWC) so maybe someone could jump in and show me my mistakes or the reasoning why they upgraded so late.
It's also quite interesting why the eye warmed while the structure in the micro wave weakened....maybe there are some infos in the internet.

Right now, numbers start to decrease and everything hints on a weakening system ( SSTs of 26-28°C just south of bangladesh, increasing shear although still weak and
internal processes ) but it is too late for any sign. weakening. This will be a very intense cyclone, affecting the coastal areas of Bangladesh

Helge