First, a confession – I’m not feeling terrifically motivated to write up this forecast. As we stumble to the end of the 2010 hurricane season, there’s a lot dry air around, there’s a minor hurricane that’s taking a track that is typical only in the late season, and it’s clear that the season will end short of forecasted ACE (Accumulated Cyclone Energy).
Even the forecast for October 13-26:
We expect that the next two weeks will be characterized by average amounts of activity
does little to add motivation.
Note on the chart above that the average hurricane activity over this period is greater than the first two weeks of August, so average activity can be enough disrupt a nice fall day!
Hurricane Paula (I have to be a bit careful here, my wife’s name is Paula) looks to be traveling along Cuba’s mountains and hence should have a short life, and add little to the seasonal total ACE. Still, average activity over these two weeks is so low that “The average forecast is due primarily to Hurricane Paula.”
The only other forecast factor of interest is the Madden-Julian Oscillation, a global wave around the tropics, currently centered between the Indian and Pacific Oceans, an area where the MJO tends to inhibit Atlantic storm development.
That’s about it. The GFS weather forecast model apparently “is hinting at the development of a system in the western Caribbean in about five days.” So even the GFS isn’t very “enthusiastic” about the forecast.
As for the previous two week period, it “was somewhat of an over-forecast. We predicted above-average ACE (>13.8 units), while only 8.2 ACE units were observed.” Except for some activity around the peak, the season struggled to get going, and a premature end seems likely.
I see the folks on top of Mt Washington in New Hampshire are giddy over snow, sleet, freezing rain, and winds that reached 98 mph (160 Km/h, about the same speed as Paula). I’m beginning to share their sense of excitement over the coming winter even though it’s still autumn here in New Hampshire and the fall foliage is at near peak conditions south of the White Mountains.
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http://wattsupwiththat.com/2010/08/10/klotzbach-on-atlantic-hurricane-season-analysis/
Klotzbach in a guest post predicted an Atlantic ACE of 185 in the August mid-season update. See above link and search the page for ACE.
The Atlantic ACE history from 1950 is interesting. The following table ranks all years by activity level and keeps the current season up-to-date. Atlantic ACE is currently 140. One big late season blow and Klotzbach might be pretty close.
http://en.wikipedia.org/wiki/Accumulated_cyclone_energy#Atlantic_hurricane_seasons_by_ACE_index.2C_1950.E2.80.932010
jorgekafkazar says:
October 13, 2010 at 4:13 pm
Pole to equator temperature gradient in northern hemisphere I recall was the hypothesis. “Global” warming isn’t uniform. The higher latitudes appear to get more than lower latitudes which reduces the temperature gradient and hence the energy available to drive extreme weather events. Seems like a reasonable hypothesis at first blush.
Dave Springer says:
October 13, 2010 at 5:02 pm
That should apply more to extratropical storms, they develop along weather fronts between relatively warm and cool air masses. When I have a chance, I’ll finish a post on an interesting site history.
Tropical storms are driven more by both the vertical temperature difference and warm SSTs. Warm water is needed to evaporate enough water to power the heat engine, and a rule of thumb is SSTs have to be at least 80°F (27°C) to develop a decent storm. Semi OT – there’s a class of extratropical storm that develops off the New England coast into something that sure looks like a hurricane. That phase never lasts long enough to investigate with an airplane, but radar images show “eye-like” structures. I suspect they really are warm core storms that are living beyond their means and rapidly reconfigure back to cold core.
October 14, 2010 at 5:51 am
…Ric…you don’t mean a polar low???????????
Staffan Lindström says:
October 14, 2010 at 10:36 am
> …Ric…you don’t mean a polar low???????????
Oops, I forgot about those. No, I don’t mean them, though they also have eye-like structures. http://www.geo-web.org.uk/PolarLow.pdf seems to be a good description.
What I’m talking about happens at lower latitudes, and while the eye has a brief life, the rest of the storm lasts for days. The official definition of “bombogenesis” (the NWS wants a better name) is a drop in surface pressure of at least 24 millibars in 24 hours.
A few links referring to bombogenesis:
http://www.theweatherprediction.com/habyhints/188/
http://www.toddgross.com/todd_gross_new_england_we/2006/12/bombogenesis_an.html
http://www.weather.com/blog/weather/8_21225.html
http://www.weather.com/blog/weather/8_13789.html (a Pacific storm with satellite photos)
Some of the links refer to a 1978 storm that stalled off of New England and remains the most impressive winter storm I’ve experienced firsthand. People find my http://wermenh.com/blizz78.html nearly every day.
Maybe Anthony could conclude this hurricane season with this paper?
http://www.worldclimatereport.com/index.php/2010/10/14/no-trend-in-global-hurricane-activity/
Reference:
Wang, B., Y. Yang, Q.‐H. Ding, H. Murakami, and F. Huang, 2010. Climate control of the global tropical storm days (1965–2008). Geophysical Research Letters, 37, L07704, doi:10.1029/2010GL042487.
Planet Earth rotates on its axis, and the atmosphere doesn’t want to turn with it, as per Newton’s laws of motion. Consequently, the roughness of the planet, surfaces above sea level, trees and other protrusions into the atmosphere of varying altitude, and even waves on the oceans move through the atmosphere, and this moves the air, and causes turbulence, and causes eddy currents to form. Just like eddy currents caused by obstructions in a river bed cause whirlpools to form, which move quite randomly, but within bounds, and dissipate as friction de-energizes the eddy currents and turbulence. Go fishing on a river and check it out for yourselves. Just as the surface level (depth of water) of a river varies because of eddy currents and turbulence, the depth/height of the atmosphere varies, causing higher and lower pressures, at the bottom of the river, for water, and at the surface of the Earth, for air pressure.
As water is an incompressible fluid, and air is a compressible fluid, the results aren’t quite the same, but seem quite close.
I have done a good deal of hydraulic engineering, so have a good bit of knowledge as to how water flows under varying circumstances.
Saying the wind blows is akin to saying the sun rises in the east. Both appear to happen, but really don’t. If, however, proper terms aren’t used, it all gets very confusing quite quickly. That is my experience as a professional civil engineer.
Of course, I am a mere engineer, not a “scientist”, but people would have gotten really annoyed had my hydraulic designs not worked.