How oil might affect a hurricane
There's no major changes to the forecast for the Gulf of Mexico oil spill. As I discussed in yesterday's post, on Sunday, the winds will begin increasing and shifting to the southeast. The latest run of the GFS model shows that this will be a week-long period of southeast winds, with wind speeds at times reaching 20 - 25 knots. These winds will threaten to bring oil to a large portion of the Louisiana coast, including regions of the central Louisiana coast west of the mouth of the Mississippi River. The Mississippi and Alabama coasts will also be at risk next week, but the risk to the Florida Panhandle is lower. Yesterday's post also has the long-range outlook for oil to get into the Loop Current and spread to the Florida Keys and beyond.
What will oil in the Gulf of Mexico do to a hurricane?
With hurricane season fast approaching and the oil spill in the Gulf of Mexico likely to still be around once hurricane season starts in June, we need to ask, how will oil affect any hurricanes that might traverse over the spill? And how might a hurricane's wind and storm surge affect the spill? Let's consider the first of those questions today.
From the time of the ancient Greeks to the days of the wooden ships and iron men, mariners dumped barrels of oil onto raging seas to calm them during critical moments of violent storms (Wyckoff, 1886.) Oil does indeed calm wind-driven waves, thanks to the reduction in surface tension of the water that oil causes. Ripples with a wavelength shorter than 17 mm are affected by surface tension, and these ripples then cause a feedback that reduces the height of larger waves with longer wavelengths (Scott, 1986.) The reduction of surface tension also impacts the flow of air above the water, and reduces the amount of sea spray thrown into the air, both of which could affect the wind speed. Oil also damps waves by forming a thick, viscous film at the top of the water that resists water motion (Scott, 1999.) Oil also helps calm raging seas by switching off of the wind energy input needed by the wave to break. This occurs because the surface film of oil prevents the generation of ripples on the exposed crests of the waves, and this smoother surface makes the wind less able to grab onto the wave and force it to break.
So, what would happen to a hurricane that encounters a large region of oily waters? A 2005 paper by Barenblatt et al. theorize that spray droplets hurled into the air by a hurricane's violent winds form a layer intermediate between air and sea made up of a cloud of droplets that can be viewed as a "third fluid". The large droplets in the air suppress turbulence in this "third fluid", decrease the frictional drag over the ocean surface, and accelerate the winds. According to this theory of turbulence, oil dumped on the surface of the ocean would reduce the formation of wind-whipped spray droplets, potentially calming the winds. The authors propose spraying oil on the surface of the ocean to reduce the winds of a hurricane. However, the turbulence theory championed by Barenblatt et al. has been challenged by other scientists. In a 2005 interview with Newscientist magazine, turbulence expect Julian Hunt at University College London, UK, remarks, "I am very doubtful about this approach." Hunt studies turbulence both theoretically and in the laboratory, and believes that the high wind speeds in a hurricane are not caused by sea spray. In an article he wrote for the Journal of Fluid Dynamics, Hunt suggests that variations in the turbulence between different regions of the hurricane cause sharp jumps in wind speed, which are responsible for the hurricane's strongest winds.
Oil reduces evaporation
Hurricanes are sustained by the heat liberated when water vapor that has evaporated from warm ocean waters condenses into rain. If one can reduce the amount of water evaporating from the ocean, a decrease in the hurricane's strength will result. Oil on the surface of the ocean will act to limit evaporation, and could potentially decrease the strength of a hurricane. However, if the oil is mixed away from the surface by the strong winds of a hurricane, the oil will have a very limited ability to reduce evaporation. According to a 2005 article in Popular Science magazine, Dr. Kerry Emanuel of MIT performed some tests in 2002 to see if oil on the surface of water could significantly reduce evaporation into a hurricane. He found that the slick quickly dissipated under high wind conditions that generated rough seas.
Figure 1. A comparison of the size of 2008's Hurricane Gustav with the size of the Gulf oil spill. The spill is only about 60 miles in diameter, while a hurricane like Gustav is typically 400+ miles in diameter.
Conclusion
A tropical cyclone in its formative stage--as either a tropical depression or a tropical storm with 40 mph winds--might be adversely affected if it encountered the Gulf of Mexico oil slick, due to the reduction of evaporation into the storm. However, a full-fledged hurricane would mix the oil into the ocean to such a degree that the storm would probably not see any significant reduction in evaporation. It remains unknown how the reduction of sea spray by oil might affect a hurricane. If the oil slick expands to a much larger size, there might be a significant reduction in strength of the hurricane, if theory of how a reduction of sea spray will decrease a hurricane's winds is correct. However, the oil slick is currently Delaware-sized, while a hurricane tends to be Texas-sized, and I doubt that the oil slick at its current size is large enough to have a significant impact on a hurricane's intensity. The slick is about 60 miles across, and it would take a hurricane about four hours to traverse the spill at a typical hurricane forward speed of 15 mph. Furthermore, the slick is within 50 miles land, and interactions with land will dominate the behavior of a hurricane that gets that close to the coast. Unfortunately, there is a decent chance that we'll get a real-world opportunity to see what will happen. June tropical storms tend to form in the Gulf of Mexico, and we've been averaging one June storm every two years since 1995. This year, the odds of a June Gulf of Mexico storm are probably a little lower than usual, shear from our lingering El Niño may bring wind shear levels a bit above average. I expect there is a 20% chance that we'll see a June tropical storm in the Gulf of Mexico that would interact with the oil spill.
References
Barenblatt, G.I, A.J. Chorin, and V.M. Prostokishin, 2005, A note concerning the Lighthill sandwich model of tropical cyclones, PNAS August 9, 2005 vol. 102 no. 32 11148-11150 doi: 10.1073/pnas.0505209102.
Hunt, J.C.R, and I. Eames, 2006, Mechanics of inhomogeneous turbulence and interfacial layers,, Journal of Fluid Dynamics, vol. 554, pp. 499519 doi:10.1017/S002211200600944X.
Scott, J.C., 1986, "The Effect of Organic Films on Water Surface Motions," in Oceanic Whitecaps, edited by E. C. Monohan and G. Mac Niocaill, D. Reidel Publishing Company.
Scott, J.C., 1999, Ocean Surface Slicks - "Pollution, Productivity, Climate and Life-saving", IEEE Proceedings of the International Geoscience and Remote Sensing Symp. IGARSS99, Hamburg, Germany, 28 June-2 July 1999, vol. 3, pp 1463-1468, 1999.
Wyckoff, A.B., 1886, The Use of Oil in Storms at Sea, American Philosophical Society, April 2, 1886.
http://www.archive.org/stream/proceedingsofamep23 amer/proceedingsofamep23amer_djvu.txt
First tropical wave of the season leaves the coast of Africa
Yesterday, the National Hurricane Center noted the first tropical wave of the year coming off the coast of Africa in their Tropical Weather Discussion. The first half of May is the typical time when the first tropical wave comes off the coast of Africa. The wave is currently positioned in the far eastern Atlantic near 5N 45W, and I don't expect it to develop, since it is too close to the Equator to leverage the Earth's spin to gain the rotation needed. The wave has quickly been joined by two new ones today, located at 15W and 36W off the African coast. Tropical waves serve as the seed that form most Atlantic and Eastern Pacific hurricanes.
Portlight delivers major aid shipment to Haiti
Portlight continues to focus its energy and funds on the situation in Haiti, where the rainy season is fast approaching the needs for shelter, medical supplies, food and water remain urgent. Their latest effort was a shipment of several thousand pounds of Durable Medical Equipment and 30,000 pounds of rice that arrived this week via the schooner Halie and Mathew.
Portlight.org is also preparing to respond the the Gulf Coast oil spill by deploying one of more mobile kitchens to feed the hundreds of volunteers likely to flood the coast when the oil finally comes ashore. Please visit the Portlight.org web site or the Portlight blog to learn more and to donate to Portlight's efforts in Haiti and the Gulf Coast.
Figure 2. Relief supplies from the schooner Halie and Mathew sitting at the Portlight Haiti warehouse, ready for distribution.
Next Post
I'm on my way to Tucson today for the American Meteorological Society's 29th Conference on Hurricanes and Tropical Meteorology, which will be held in Tucson next week. My next post will probably be on Monday night, when I plan to discuss the record SSTs observed last month in the tropical Atlantic. I'm excited to be catching up on and blogging about all the latest advancements in hurricane research!
Jeff Masters
Reader Comments
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Regarding the SOI.... 11 is not really "tanking"....since it only peaked at 15, and the SOI likes to do its work in swings of up and down. It rarely stays steady at any value for very long. It will likely go down a bit and then go back up, but the 90-day average is now 0, and this positive burst has been pretty insane, and very La Ninish.
Regarding the Kelvin Wave.....it actually just recently made it all the way across the Pacific. Remember the tropical disturbance I was watching? That was directly a result of the Kelvin Wave bringing westerly low-level winds into the eastern Pacific, and you can see they are still there in the 7-day average:
These winds have continued to prevent upwelling in the eastern Pacific, which is why cold water isn't making any progress towards the surface right now. It will eventually though.
500mb height anomalies May 1st-May 5th:
Current AVHRR SST Anomalies as of May 7th:
didnt Dr M just post yesterday that he felt we would not see a June storm likely because of the lingering El Nino?
What are your thoughgs on that Levi?
Here's BBC Weather with Ash Cloud Forecast.
Link
TGIF!
Whether or not June conditions will be favorable in the Gulf of Mexico nobody can really know quite yet, but I disagree with Dr. Masters' statement that lingering El Nino effects will cause unfavorable conditions.
Again, and I'll keep driving this point home, this El Nino is atmospheric-driven, meaning that the water responds to the atmosphere, not the other way around. This is why the SOI, an atmospheric index, spiked and THEN the waters started cooling. Thus, there is no "atmospheric lag", and atmospheric conditions are already starting to resemble a La Nina more than an El Nino. It is really amazing how fast this turnaround has been occurring. We are already at a neutral signal overall with cold water appearing in the central Pacific, and the atmosphere is screaming La Nina right now with the 90-day SOI up to zero. We will already be entering a weak La Nina in June.
We're under the gun tonight, especially areas north of us.
I'm closely watching the Gulf of Guinea here...as it was struggling to thrust a cold tongue of water up along the African coast but this has faded over the last 5 days. It is a war between the European and the CFS over what water temperatures will be like this summer in the south Atlantic. The Euro is cold and the CFS is warm.
well I believe he was talking more in terms of shear in the Gulf of Mexico being unfavorable in June due to lingering El Nino conditions
Yes I know, that is precisely my point. There is no "lag" or "lingering effects"....the atmosphere is already slamming head-first into La Nina....thus there shouldn't be any "lingering wind shear" due to El Nino. The atmosphere is leading the ocean, so there are no "lingering effects".
Ah ok, personally I think we get a hurricane in June, tops 85mph
My my my.....it is amazing to see this unfold. Sure enough the reversal to a ridging pattern over the eastern US and Caribbean during the past week has raised Gulf of Mexico SSTs at a dizzying rate. We were still all blue colors, below normal at the end of April, and now look at it! Simply amazing.
Lol Levi....I am in North Florida near the Gulf and, yes, it basically went from Spring to Summer around here in the last week.....I know you are in Alaska reading the charts.... :)
You may want to see this then.
El Nino 3.4 drops bigtime however, El Nino 1-2 and 3 go up,but Levi32 explained very well about why the warm waters continue east of 120W.
Wow that's neat....thanks! Will be interesting to see if that unfolds.
Afternoon Storm :)
Great shot, thanks for posting. There are new cameras online on the porolfsfelli-site,
f.e. a live cam with heat images:
*cloaks*
I like beach twister better Pat. Nice sentiment though...
3 miles SSE of Christmas, Orange County.
Thunderstorm wind damage, reported by Park/Forest srvc.
Lots of large tree limbs down in Tosohatchee Wildlife Management Area.
05/06/2010 0338 PM
6 miles SSE of Christmas, Orange County.
Funnel cloud, reported by law enforcement.
Funnel cloud sighted by Florida department of transportation crew near intersection of sr 520 and sr 528.
In contrast, surface pressures were below-normal in these areas in March, when the El Nino was still dominant.
Too early for the A-B to set in place, but, if this ridging persists and it were to stay in the current general vicinity going into August and September, you basically have a bee-line from Africa to the Antilles.....
Good thing too.
Pretty amazing to see
What does that mean? I'm guessing that it's a signal that La Nina is fast approaching, but certainly not sure.
Where did you find that out?
If the Gulf of Guinea cools then precipitation will increase in the northwestern Sahel region reducing SAL.
Interesting. Seems like the closer we get to hurricane season, the more things look favorable for an extreme season. The persistent ridging over the Eastern seaboard the past week or two is alarming. I hope it's not a pattern that persists into the heart of hurricane season. Also, it's beyond amazing to see how most of the Gulf has gone from well below average temps to slightly above average in just a couple of weeks.
Your a bit behind...
IMO I think we'll be higher....
Hi Storm. The upper level ridging you mention, is that part of the Bermuda High, ( I thought that was lower level) I remember someone said upper ridging is good for hurricanes? Or am I completely backwards again? Lol. Just wondering why you don't like it. What I don't like abut ridges is being on their western side. :)
Can anybody tell me what the second chart on 148 is showing? Thanks. :)
CFS forecasted wind shear anomalies....blue being below-normal and red being above-normal.
The Bermuda High is a semipermanent deep-layered high pressure system.......meaning that high pressure extends up through the entire atmosphere, from bottom to top. Thus, when referring to the Bermuda High we can be referring to either the surface high or the mid-upper high, but they are both usually stacked on top of one-another.
Upper highs are indeed good for hurricanes, but only the very upper ones, around 200mb. Anything lower than that, say, 500mb, would represent an area of large-scale sinking, and that is not favorable for storms trying to develop. However, a high at 200mb is near where the tops of tropical thunderstorms are, and a high at that level provides an easy way for air at the top of the thunderstorms to be transported outwards in all directions, allowing more air from the surface to more easily rise and fuel more thunderstorms.
You usually don't see a hurricane develop directly beneath the Bermuda High. We all know that most hurricanes get steered around the southern and western periphery of the Bermuda High, but not right under it. This is because the Bermuda High is a region of intense sinking air, and is why the eastern Atlantic north of about 20N is nearly always completely dry.
Ah ok thanks. So they look like their shutting the gulf down for the season? I could live with that. But that doesnt seem to gel with what I'm hearing.
Oh ok. That makes sense. I had it half right. But now I know why. Thanks :)
volcano mad?? Look at this web-cam in the link below:
Link
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