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Posted at 10:45 AM ET, 09/23/2009

Lackluster Hurricane Season Could Stay That Way

By Greg Postel

* Where's Fall? Our Full Forecast | NatCast | Classic D.C. Sunrise *


Tracks for the six named storms (and Tropical Depression One, which failed to reach tropical storm strength) so far this hurricane season. Courtesy Unisys.

So far the 2009 hurricane season has produced only six named storms, two of them hurricanes (Bill and Fred).

Though these numbers aren't dramatically low for late September, meteorological conditions over the tropical Atlantic will continue to give incipient disturbances little chance to flourish in the remaining days of the month. In fact, I wouldn't be surprised to see even the latest predictions for a quieter-than-normal season fall short.

Keep reading for more on the outlook for the rest of the 2009 hurricane season...

Stronger-than-average wind shear in the Atlantic Ocean has no doubt hindered the development of tropical cyclones thus far. These changes in wind speed and direction with height have been able to dismantle many of the budding disturbances that have dared to evolve into coherent systems. It's safe to say that the current El Nino episode -- the warming of the waters in the central and eastern Pacific Ocean -- is consistent with the lack of hurricane activity in the Atlantic.

Another, though not necessarily unrelated, reason for our relatively benign hurricane season can be linked to the unusual dryness of the atmosphere over the Atlantic, particularly at altitudes where air is often pulled into a developing storm. Research has shown that the penetration of relatively dry air into the core of a tropical system can have devastating effects on the health of its circulation. By generating cool, dry columns of downward-moving air in the lower levels of a storm, this process can block the intake of warm, humid air that is essential for its survival.

The plot below shows the relative humidity anomalies (departures from average) in the Atlantic at about one mile in altitude for the month of August. The regions shaded in yellow and red indicate conditions much drier than normal. Though a time-averaged plot like this does not necessarily yield insight into what happened during any single event, a case-by-case look at the tropical systems this year pretty much tells the same story; that is, just about every disturbance we've tracked has had to fight off the choking effects associated with the inhalation of a nearby layer of dry air originating from Africa.


See paragraph above image for explanation. Courtesy NOAA.

Unless the air over the tropical Atlantic moistens up, and the winds become more favorable for storm development, the final hurricane count will be underwhelming. The door is slowly closing on the 2009 season.

By Greg Postel  | September 23, 2009; 10:45 AM ET
Categories:  Tropical Weather  
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Comments

I would have been greatly surprised if we had anything like 2005 this year!!!

As has been pointed out numerous times, we're in an "El Nino" fall which historically is NOT GOOD for Atlantic/Caribbean tropical cyclone development. Look to the Eastern Pacific for tropical cyclones this fall; there have been a few good ones out there.

Posted by: Bombo47jea | September 23, 2009 11:52 AM | Report abuse

Looks like all the doomsdayers of 2005 who moaned about "global warming" and predicted that, because of it, 2005's record hurricane season would be the start of massive and destructive seasons have had to eat a LOT of crow the last 4 years. The last four North Atlantic seasons have been some of the tamest that I can remember....especially this year.

Posted by: MMCarhelp | September 23, 2009 1:22 PM | Report abuse

MMCarhelp,

Those who more clearly understand the implications of global warming are not surprised by the recent hurricane season variability.

greg

Posted by: gregpostel | September 23, 2009 2:38 PM | Report abuse

Greg,

You nailed it. With global warming having stalled, combined with the El Nino and other weather effects, its no surprise that this season is light.

Posted by: RMVA | September 23, 2009 5:21 PM | Report abuse

That may be true, Greg (or at least partly true), but that's not the kind of stuff we were hearing 4 years ago from the global-warming doomsday crowd. To believe them, we were going to have a more or less constant barrage of level 3, 4, and 5 storms during the future hurricane seasons. The facts turned out quite differently.

I'm not going to constantly post anti-global warming stuff on CWG every day like Mr. Q does (he clearly goes to extremes) but it is clear that much of the stuff about global warming is more hype than fact.

Posted by: MMCarhelp | September 23, 2009 6:24 PM | Report abuse

The writing seems to have been on the wall for a bit regarding this season. If nothing else, the early recurves argued for a potential of that continuing. Since the burst of storms -- and Fred, everything has been looking rather meager. With El Nino making its mark it's going to be harder to get the late-season threats from the Caribbean. Gulf of Mexico seems to be the main threat but there has not been much there all year so if it stays inactive it would not be surprising.

The ghosts of 2005 will likely haunt us for some time yet. Lots of wild speculation following that season -- and of course the dual cat 5 hits on Mexico two years later -- has mostly not verified in the Atlantic basin since. Just last year both Ike and Gustav were hyped by many sources as they entered into the Gulf and they did not "go Katrina."

I have noted more and more reference to the SAL over recent years. I can't remember which season it was, probably 06 (?) where it was also an issue throughout. I'm sure there have been studies, but I'd like to know if that has become more common over recent times. If so, it seems it could counteract some of the general warming predicted by supressing activity on the whole.

Hard to argue we are not in an up-cycle overall (at least partly natural throughout the course of hurricane history) in recent times, even if we probably won't ever see another 2005.

Posted by: Ian-CapitalWeatherGang | September 23, 2009 8:26 PM | Report abuse

@MMCarhelp

2008 was quite an active season with 16 named storms and 5 major hurricanes. So careful with you last four year generalization. Am with you re: 06,07, and 09...

Posted by: CapitalWeatherGang | September 24, 2009 1:08 AM | Report abuse

MMCarhelp,

" ... it is clear that much of the stuff about global warming is more hype than fact."

What stuff ?

Just read the science and you'll be fine.

Or, if you feel otherwise, submit a research paper to the scientific journals and tell them where they're wrong.

Posted by: gregpostel | September 24, 2009 10:43 AM | Report abuse

Greg - Nice post. Any stats on what's been going on in the Pacific? Just curious. Thanks!

Posted by: Andrew-CapitalWeatherGang | September 24, 2009 4:36 PM | Report abuse

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