BoB: AMPHAN - Post-Tropical

[aspen]

It couldn’t choose between a pinhole or a normal eye.

[SouthDadeFish]

And now GPM with a little better resolution. Looks like it tried to develop concentric cores. Probably won't be rapidly intensifying until it sorts that out.

https://i.imgur.com/nBFnVwL.jpg

https://i.imgur.com/R4N8Eze.jpg

Looks like some signs of easterly shear too. The inner eyewall is relatively asymmetric. This could be another inhibitor of more rapid rates of intensification. Hopefully the shear persists.

[Chris90]

Well isn't there a wide range of intensity estimates going on. 40kts all the way to 100kts+. I think it's probably good that Maue didn't go into something like investment banking with how bullish he usually is.

Based on microwave, I'd say it's probably a Cat 1 right now, between 75-80kts, since it does have a rather small, tight core with a partial eyewall, but it's also surrounded by what appears to be a larger, partial eyewall. If it can focus all the energy into that small core and finish that eyewall, those model runs could definitely come to fruition. Let's hope it doesn't.

[1900hurricane]

And now GPM with a little better resolution. Looks like it tried to develop concentric cores. Probably won't be rapidly intensifying until it sorts that out.

https://i.imgur.com/nBFnVwL.jpg

https://i.imgur.com/R4N8Eze.jpg

Looks like some signs of easterly shear too. The inner eyewall is relatively asymmetric. This could be another inhibitor of more rapid rates of intensification. Hopefully the shear persists.

You wouldn't know it by looking at WV imagery, but guidance does indicate a wind maximum near 200 mb, which would actually be under the anvil level in this case due to the very high tropopause. It definitely bears watching as guidance (particularly the GFS) only increases it as time goes on. Statistical intensity models like SHIPS and LGEM have not been very excited about this one, and that may be a big reason why.



*EDIT to include graphic I forgot.

[shah83]

2100z image does look like inner eyewall will be winning this one. Maybe the easterly shear was only temporary?

[shah83]

Latest GFS has much weaker system, apparently because shear will be an issue all the way north.

[aspen]

Really nice microwave pass showing the double partial eyewalls, from ~19z: https://rammb-data.cira.colostate.edu/t ... 161941.gif

[aspen]

I’m seeing two options for Amphan right now:

1.) the outer eyewall is able to take over and solidify, and Amphan begins to rapidly intensify as early as tomorrow. This decent large core should prevent absolute ludicrous intensity like Hagibis, but it would probably be able to take advantage of the extremely favorable waters of the BOB, before potentially increasing shear puts a lid on that intensification.

2.) Amphan attempts to repair its core and rapidly intensify, but shear will continue to disrupt it, so it won’t be able to take full advantage of the high SSTs/OHC. In this scenario, I’m thinking it would peak as a somewhat sloppy Cat 3, maybe a low Cat 4, and continue to fluctuate in intensity as it approaches landfall.

[shah83]

As of 0145z, eye is out. Amphan is ready to rumble, it looks like.

[aspen]

As of 0145z, eye is out. Amphan is ready to rumble, it looks like.

I don’t think that’s the eye just yet; it seems to be a warm spot. The actual center seems to be slightly displaced from the blob of <-90 C cloud tops.

[shah83]

Looking at the new 2357z microwave, does sort of feel like there is an almost complete eye feature, even if it's weak on the east side.

[Yellow Evan]

As of 0145z, eye is out. Amphan is ready to rumble, it looks like.

Given how lopsided Amphan is as a whole, I don't agree.

[shah83]

GFZ 00z run delivers a catastrophic blow to West Bengal and Bihar.

[shah83]

Canadian and Ukmet does the same.

edit, well, they actually strike at the border between India and Bangladesh

[Kingarabian]

I'm not familiar with the geography that Amphan will likely affect. Is there currently a best case scenario that can happen other than it significantly weakening before landfall? Like are there less populated regions in its path? India has the 2nd highest population in the world.

[shah83]

I'm not familiar with the geography that Amphan will likely affect. Is there currently a best case scenario that can happen other than it significantly weakening before landfall? Like are there less populated regions in its path? India has the 2nd highest population in the world.

If Amphan hits primarily at the border between India and Bangladesh, then a wildlife refuge/mangrove forest will blunt some of the surge impacts. As you can see with the Canadian rainfall prediction, much of Bangladesh, including Dhaka, would get tremendous rainfall and would probably be severely flooded by the combination of surge traveling up the Meghma river and rainfall coming in through the river/creek system. It would be a bit similar to Cyclone Sidr, except this is probably going to be a bigger storm. Cyclone Sidr still killed between 3k and 15k people, though.

For practical purposes, the best case scenario is lots of shear and the storm getting far enough west to hit Andhra Pradesh at Cat 2-3 intensity.

The GFS is definitely one of two worst case scenarios, the other being the cat-5 landfall just north of Chittagong.

[shah83]

getting quite a bit of dry air around it now.

[doomhaMwx]

Upgraded to a cat 1 and SCS by JTWC and IMD, respectively.
I wonder if this will weaken as much as JTWC forecasts while approaching the coast. I have seen such forecasts for some NIO cyclones these past few years, but they ended up hitting land at/near peak.

[Nancy Smar]

Severe Cyclonic storm AMPHAN lies over central parts of south Bay of Bengal. To intensify into very severe cyclonic storm during next 12 hours and cross West Bengal and Bangladesh coast during 20th afternoon/evening

[Nancy Smar]

SALIENT FEATURES:-
VORTEX (AMPHAN) OVER SE BAY & N/HOOD :-
VORTEX (AMPHAN) OVER CENTRAL PARTS OF SOUTH BAY & N/HOOD HAS
FURTHER INTENSIFIED NOW LAY CENTERED NEAR 11.7N/86.0E (.) A BANDING
EYE IS OBSERVED IN THE VISIBLE IMAGERY. INTENSITY T4.0 RPT T 4.0 (.)
CURVED BAND PATTERN (.) ASSTD BKN LOW/MED CLOUDS WITH EMBDD INT
TO V INT CONVTN OVER BAY BET LAT 7.5N TO 14.0N LONG 81.0E TO 89.0E
(.)

The latest Dvorak analysis from IMD is T4.0 so that Amphan could be classified as a VSCS later today.