Hurricane Julia explodes — Atlantic has two coincident Category 4 hurricanes, very rare

Oh no – it’s exactly as we thought. CAGW is spawning unprecedented storms which will only provide a temporary reprieve from the catastrophic warming to follow. Donations gratefully accepted.

Impressive! Patterns like this one are unsustainable though. It should change in a week or so, especially if moisture in the Indian Ocean keeps retreating east away from the East coast of Africa, as it is doing now. Tropical activity should shift to the Caribbean and (hopefully not) the southern Gulf of Mexico.

Are the wind speeds for Julia estimates from satellite photos and estimated pressure numbers or did a hurricane hunter aircraft actually fly in and measure them?

While having two cat 4s simultaneously is almost without precedent in our records, let’s remind ourselves that since the satellite era, we now have the ability to identify hurricanes in the open ocean far from land, and to accurately classify their wind speed.
Chris Landsea was lead author of an article about a year ago showing that there has been no upward trend in the number of hurricanes per decade hitting land, and that the decades which featured the largest numbers of major hurricanes were in the 1800s. I think WUWT even had a blog on the article. Those results contrasts with what you get with the satellite record, where there are upward trends in the last few decades. That upward trend is an artifact of the satellite record, where we now identify hurricanes which live and die hundreds of miles from land.
So here is a question: if this were 1920 or 1950, would we know that either of these hurricanes was a class 4? If I had to guess, it is possible that in 1950 there would have been enough ships to have intersected Igor to say “yes”, but that isn’t a given. However, if Julia doesn’t stay a class 4 for very long, given where it currently is, far from shipping lanes and only recently a major hurricane, I would guess that we would never know that it was a class 4. If it degrades to a cat 1 in a few days and turns north well east of Bermuda, how possible is it that we might not have known of its existence?
So perhaps it would be better to say that it is unprecedented — in the 30 or so years of the satellite record — to have two cat 4s in the N Atlantic.
That said, it does appear to be consistent (there’s that dreaded word again) with the notion that in a warmer world there will be more powerful hurricanes.
The counter argument, as Ryan Maue has said before, is that the total ACE in the N Hemisphere, and in the world, had NOT been trending upward, with the largest ACE amounts since 1979 occurring in 1993 and 1998. That isn’t so consistent with the idea of ever more powerful storms.
Bottom line: two cat 4s at the same time is pretty impressive, but I don’t want to take any climate change implications just yet.

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ryan: just wait for the Arctic blast behind Igor during the next 5-7 days over the Northern half of the US and Canada. Time to harvest your tomatoes…
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The pulse of big blobs of tropical moisture & rain northward is often counteracted by a similarly large pulse of cold air southward to follow behind it. The passage of Hugo in VA years ago caused frosts in late Sept, well before the average first-frost.

Scott B says:{September 15, 2010 at 5:09 am}
“@Tom in Florida:
The wind speeds and pressures for Julia and Igor are just from satellite estimates. ”
Exactly, so when it is reported that this is the only the second time we’ve had two Cat 4 storms together, one must take it with a grain of salt. Prior to satellite coverage how would one know if this hadn’t happened more than once before, especially so far out in the Atlantic.

Ryan,
Thanks for the update. I’m also enjoying the pacific coastal fog while marveling at these Atlantic storms.
Perhaps the lack of big storms in August increased the odds of multiple majors since the ATL basin has remained relatively free of upwelling. 2005 conditions were also ideal for development but the constant parade of storms created too much competition limiting the chances for concurrent majors. It reminds me of my storm chasing days when the best supercells seemed to occur close to sunset on the days when there was no activity anywhere during the afternoon.
With tropical Atlantic SST anomalies near record highs and a developing La Nina, have you looked into the possibility that we could be setting up for a significant farm belt drought next year? I know there have been studies suggesting the dust bowl years were characterized by a large tropical SST differential between the Pacific and Atlantic basins (cool Pacific, warm Atlantic). Does the current situation and forecasts bear enough similarity to that of the 1930’s that we should be concerned?
ryan: The SSTs are above average, but storms do not form due to the SST anomaly. It is likely that the atmospheric conditions of lower vertical shear allowed the African easterly waves to organize quicker than normal. When they come off of Africa with low-level circulations already (like midwestern US mesoscale convective systems) in La Nina years, they develop quickly. But the Cape Verde season is relatively short, and only a few more weeks of activity out there is normal.
Similarity in climate — as with analogs in weather — is a risky business. You can never have the exact same climate conditions in terms of SST patterns, and then there is no guarantee that the nonlinear feedbacks will even operate in the same sign let alone the same way. Think of the radically different forecast tracks of a hurricane you get with different weather forecast models…

To giant-heat sucking vacuums in the North Atlantic at the same time. As others have said this has probably happened before-but better detection is the operative word here…

Wouldn’t call this unprecedented unless qualified with “in the historical record”. It’s not like the pilgrims could see what was going on in the Atlantic by standing on the shore with a good eye-scope. Given the long history of the present location of the Atlantic, it stands to reason this has happened before.

rbateman
September 15, 2010 at 3:38 am
“Have any 2 hurricanes ever hit the same place in rapid succession?”
I seem to remember Florida getting slammed pretty hard by a couple right in a row during the mid 90s. I think one even went over the panhandle and hooked back for a second chance at destruction. I’m gonna havta google it when I get home tonight.
BTW, Me and a few co-workers were talking about the possibility of a late season, with all of the major energy coming after the halfway point, but having three systems with two huge ones, and one of those nearing gigantic, just, well, blows me away.
ryan: the past 60-years when taking account El Nino and La Nina: no discernible correlation between activity during the first half and the second half of the season. it’s a crapshoot…