LA NINA:Why all the Shear ?

[bucman1]

Although we are in a LA Nina, the shear in the tropics are incredible, Why?

It suppose to be the complete oppisite?

[boca]

Their was an article posted in the Sun Sentinel about why all the shear. Here's a snippet from it.
Rather, thank a thing called the "mid-oceanic upper tropospheric trough," said Gerry Bell, lead hurricane seasonal forecaster for the National Oceanic and Atmospheric Administration.

"That's been fairly well defined this year and it's been fairly persistent, fortunately," he said. "That has been shearing these tropical systems."

The trough, an area of low pressure about 35,000 feet up, is a normal feature of the atmosphere. Some years it is stronger than others, regulated by conditions such as El Niño and its meteorological opposite, La Niña, he said.

During this storm season, the trough has been robust over the Caribbean as well as the Atlantic, Bell said. As a result, September, a month that normally produces the most powerful storms, was limited to two Category 1 hurricanes in Humberto and Lorenzo. Both briefly emerged in the Gulf of Mexico before striking land.

[Derek Ortt]

that was after it allowed 2 cat 5s to roam the Caribbean

[deltadog03]

This should PROVE That the weather dosn't always do what "its suppose" to do.

[Honeyko]

I don't recall ever seeing a tropical storm as big as Karen on a west-northwesterly under 20N heading ever getting killed in September.

[CrazyC83]

One thing to remember: even in 2005, Cape Verde struggled, as most of the storms were homegrown or higher-latitude systems...

[HurricaneBill]

One thing to remember: even in 2005, Cape Verde struggled, as most of the storms were homegrown or higher-latitude systems...

True. The only Cape Verde storm to become a hurricane was Irene, and she struggled throughout most of her trek across the Atlantic.

[Category 5]

One thing to remember: even in 2005, Cape Verde struggled, as most of the storms were homegrown or higher-latitude systems...

True. The only Cape Verde storm to become a hurricane was Irene, and she struggled throughout most of her trek across the Atlantic.

Not true. Cindy, Dennis, Emily, Katrina, and Rita all had Cape Verde ties.

As for this year, it hasn't been friendly for long track CV storms, however, 2 storms of cape verde origin have got into the Caribbean, look how that turned out. Both of them Category 5's.

Climatologically speaking, the window for long track CV storms should be closing, however, you just never know.

[Coredesat]

Actually, Rita developed from the interaction of an old front and a tropical wave, so it doesn't really have CV "ties" so to speak (if it did, all storms forming from waves would have CV ties). Dennis wasn't a CV hurricane, and neither was Katrina (since it formed from the MLC of TD 10L and a tropical wave). Cindy wasn't a CV hurricane, either - it developed just south of the Yucatan.

2005's only CV hurricanes (or hurricanes that fit the definition of a Cape Verde-type) were Emily and Irene.

[Matt-hurricanewatcher]

It has been very unfavorable for long tracking cape verdes since 2004. Dean got lucky and felix did not really get going intill it got into the caribbean.

[Matt-hurricanewatcher]

[Ptarmigan]

I wonder if North Atlantic Oscillation plays a factor in this one as well? I noticed in 2005, there was a monsoonal trough, which you don't see often. 2005 had lots of homegrown storms that formed rather close, not too many CV storms. 2004 had more CV storms. One interesting thing to point out, some active seasons barely had any storms forming the Caribbean, notably 1936. Every year, some parts of the Atlantic is more active than other parts. I know monsoon plays a role in tropical cyclone formation worldwide. If I am correct, the North American Monsoon is part of the reason why EPAC is one of the most active basins besides WPAC and SIND.

[Category 5]

Actually, Rita developed from the interaction of an old front and a tropical wave, so it doesn't really have CV "ties" so to speak (if it did, all storms forming from waves would have CV ties). Dennis wasn't a CV hurricane, and neither was Katrina (since it formed from the MLC of TD 10L and a tropical wave). Cindy wasn't a CV hurricane, either - it developed just south of the Yucatan.

2005's only CV hurricanes (or hurricanes that fit the definition of a Cape Verde-type) were Emily and Irene.

From the post storms

The tropical wave that eventually developed into Cindy moved westward off the coast of Africa on 24 June.

Dennis formed from a tropical wave that moved westward from the coast of Africa on 29 June.

The complex genesis of Katrina involved the interaction of a tropical wave, the middle tropospheric remnants of Tropical Depression Ten, and an upper tropospheric trough. This trough, located over the western Atlantic and the Bahamas, produced strong westerly shear across Tropical Depression Ten, causing it to degenerate on 14 August approximately 825 n mi east of Barbados. The low-level circulation gradually weakened while continuing westward, and it eventually dissipated on 21 August in the vicinity of Cuba. Meanwhile, a middle tropospheric circulation originating from Tropical Depression Ten lagged behind and passed north of the Leeward Islands on 18-19 August. A tropical wave, which departed the west coast of Africa on 11 August, moved through the Leeward Islands and merged with the middle tropospheric remnants of Tropical Depression Ten on 19 August and produced a large area of showers and thunderstorms north of Puerto Rico.

Rita originated from a complex interaction between a tropical wave and the remnants of a cold front. The tropical wave moved off the west coast of Africa on 7 September

[btangy]

La Nina doesn't guarantee that shear will be below normal. Rather, it shifts the probability distribution such that there is a higher probability of lower than normal shear. On any given day, in any given spot, and even over the entire season, shear can still be above normal due to random chance.

For example, So Cal had one of its driest winters ever last year despite it being an El Nino year. Nothing is guaranteed in a chaotic system.