Tropical Cyclone Gonu & the Indian Monsoon Onset Vortex

[philnyc]

I was looking for the start of the Indian Monsoon and then got distracted by Gonu. Here is what I finally noticed:
At first we had an early start to the monsoon along the immediate SW coast at Kerala. Please use the following link to follow the referenced images: http://www.satmos.meteo.fr/cgi-bin/qkl_ ... 07&mois=06 In the 05-29 water vapor satellite we can see the northward progressing ITCZ enveloping all areas from SE Asia across southern India to Africa. What's quite interesting is that the onset vortex in that image that started up the monsoon appears to have then drifted NW and is the same one that developed into Gonu. At first, as a weak depression around 05-29, it enhanced the SLLJ (Somali Low Level Jet) and brought monsoon rains to Kerala. But as soon as it drifted a few hundred miles away from the west Indian coast and deepened into a strong depression, it had the opposite effect, by diverting and cutting off the SSLJ, effectively blocking the moisture flow into southern India - in the 06-02 water vapor satellite we see the water vapor content over India has dropped significantly. The stronger the cyclone got, the more low level high theta-e air it diverted into its own circulation. Between this time and the time it became a cat 5, the monsoon's progress had completely halted – see the 06-04 water vapor satellite and notice that the belt of moisture associated with the ITCZ is pretty much gone from the western Bay of Bombay to the central Arabian Sea. But notice today's satellite images of the Indian Ocean show that now that Gonu has practically died out, the monsoon has blossomed over all of south India. We are back on track. Interesting stuff: The onset vortex that started up the monsoon developed into a monster cyclone that shut it off. Wow! This is my first post at STORM2K so I didn't know how to insert images. I especially need to show the 850mb charts to show why the SSLJ (Somali Low Level Jet) got disrupted. I will post more images when I get this format down...

[Chacor]

Welcome to S2k!

Yes, I've seen a news report saying that Gonu was to blame for blocking/delaying the Indian Monsoon, which is desperately needed this time of year to cool temperatures down. To add an image in, just use

Code: Select all

[img]URL of image.jpg[/img]


[Aslkahuna]

BTW that was technically not the ITCZ (the convergence zone between the Trades of the Northern and Southern Hemisphere) but rather the Monsoon Trough that was moving north. The Monsoon Trough has westerlies on the equator side and the Summer Hemisphere Trades on the poleward side with characteristic cross equatorial flow. Within the trough we have lower pressures light winds and light vertical shear with good horizontal cyclonic shear-formation heaven. The horizontal shear in the low levels can provide enough low level vorticity even in low latitudes to counteract the absence of Planetary Vorticity (Coriolis). The high level and strong easterlies above the monsoon flow on the equator side of the trough can enhance outflow form a Cyclone should its own outflow connect to it and if the storm becomes strong enough it can pull the trough north and enhance the monsoon flow-been in enough of those cyclone generated monsoon surges when I was in the Philippines.

Steve

[Patrick99]

That's the thing about those strong hurricanes...they vacuum a lot of moisture. I dread having major hurricanes miss us to the north and east, because that always makes for very hot conditions. In August and September, you do *not* want a clear blue sky all day long. It's unbearable.

[Ptarmigan]

That's the thing about those strong hurricanes...they vacuum a lot of moisture. I dread having major hurricanes miss us to the north and east, because that always makes for very hot conditions. In August and September, you do *not* want a clear blue sky all day long. It's unbearable.

I know that from experience. It is always hotter and drier.

[Typhoon Hunter]

That's the thing about those strong hurricanes...they vacuum a lot of moisture. I dread having major hurricanes miss us to the north and east, because that always makes for very hot conditions. In August and September, you do *not* want a clear blue sky all day long. It's unbearable.

That's very interesting. I remember clearly just prior to Super Typhoon Haitang making landfall on Taiwan in July 2005, my friends in Hong Kong and Guangdong were moaning badly about the terrible heat conditions. Haitang was a large system and contributed to southern China's hellish hot conditions at that time.

[Ptarmigan]

Welcome to Storm2K. Interesting article.

[Aslkahuna]

The sudsidence around the periphery of the hurricane (particularly mature storms) as the outflow descends to lower levels is what give the clear and hot conditions ahead of the storm. In the Philippines, when a storm would pass to our north and northeast, we would usually get the tail of enhanced monsoon flow which would result in overcast conditions with heavy rains and coastal squalls.

Steve

[philnyc]

Welcome to Storm2K. Interesting article.

Thanks. I already love this site.

[philnyc]

BTW that was technically not the ITCZ (the convergence zone between the Trades of the Northern and Southern Hemisphere) but rather the Monsoon Trough that was moving north. The Monsoon Trough has westerlies on the equator side and the Summer Hemisphere Trades on the poleward side with characteristic cross equatorial flow. Within the trough we have lower pressures light winds and light vertical shear with good horizontal cyclonic shear-formation heaven. The horizontal shear in the low levels can provide enough low level vorticity even in low latitudes to counteract the absence of Planetary Vorticity (Coriolis). The high level and strong easterlies above the monsoon flow on the equator side of the trough can enhance outflow form a Cyclone should its own outflow connect to it and if the storm becomes strong enough it can pull the trough north and enhance the monsoon flow-been in enough of those cyclone generated monsoon surges when I was in the Philippines.

Steve

Thanks for the great reply, Steve. Good point about the monsoon trough. I realize the winds are easterly on both sides of the ITCZ as they converge but for the monsoon trough are westerly on the equatorward side and easterly on the poleward side. That gives you cyclonic shear. That is of course a big difference. Thanks for clarifying that. But the ITCZ does move northward of course over the summer months into the northern hemisphere, as well as the monsoon trough, no? I also thought the monsoon trough develops on the poleward side of the ITCZ as the easterly winds on the northern side of the ITCZ veer to westerly due to the Coriolis force; i.e. the winds moving westward on the northern side of the ITCZ turn northeastward and then eastward and it is the interaction of these east-northeast winds on the northern side of the ITCZ with the westward moving trade winds north of them that causes the cyclonic shear. Doesn't the ITCZ in a sense allow the monsoon trough to happen? Or am I missing something?

[Aslkahuna]

The westerly flow in the equator side of the Monsoon Trough develops as a result of cross equatorial flow around a buffer ridge that develops along the Equator to the east. The SE Trades of the Southern Hemisphere don't begin to converge with their northern counterparts until you get towards the Central Pacific. The Westerly wind burst associated with the MJO are also role players as they appear to be the source of straight line Monsoon surges that occur without cyclonic development (though they can eventually lead to such development. I use to do streamline analyses when I was a forecaster in the Philippines and it was always intersting to watch that flow across the equator during both Monsoons-the Summer and Winter.

Steve

[wjs3]

Phil--

Welcome to S2K. Glad to have you here. You'll love it.

WJS3

[philnyc]

Thanks! I think I know who you are.

[philnyc]

Thanks, Steve. This is really interesting stuff to me. I just learned about the westerly wind bursts last year in class, and I find it fascinating. Although they are quite detectable once they get going, they are actually fairly hard to forecast, right?

[wjs3]

Thanks! I think I know who you are.

Ha. yeah.

Hey Phil, if you are up for it, you should post a couple of the monsoon-related things you have done here--the one you are wokring on right now and the one you did last year for class. A lot of people here would really enjoy them.

WJS3

[philnyc]

Thanks! I think I know who you are.

Ha. yeah.

Hey Phil, if you are up for it, you should post a couple of the monsoon-related things you have done here--the one you are wokring on right now and the one you did last year for class. A lot of people here would really enjoy them.

WJS3

Thanks, Winn. I might just do that.

P.S. You were so right. It's great on here. The only thing is, it reminds me of when I got Playstation2. I got addicted to Ratchett & Clank so fast that I wasn't heard from by friends or family for months!

[wjs3]

Phil, just wait until you see the place with several hundred people on the boards if we get a really active period as happened in 04 or 05. It's unbelievable here. Real time analysis of Recon, following every model run right as it comes out. Frame by frame satellite analysis, surface obs at landfall, wowee...and thank goodness, the pro mets to keep us all in line. As you've already seen from Steve, the pro mets around here are great and help us all learn.

Great stuff.

WJS3

[philnyc]

Amen. I can't wait for the action to start. I've been following that wave, as you probably have seen. Even though we know it's got almost no chance, it seems to bode for a really intense season...

[philnyc]

Welcome to S2k!

Yes, I've seen a news report saying that Gonu was to blame for blocking/delaying the Indian Monsoon, which is desperately needed this time of year to cool temperatures down. To add an image in, just use

Code: Select all

[img]URL of image.jpg[/img]


Thank you!