Loop Current Eddy cuts off; oil danger to Keys now greatly reduced

By: Dr. Jeff Masters , 2:24 PM GMT on May 28, 2010

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A major ocean current re-alignment is underway the Gulf of Mexico right now, and the new configuration that is developing greatly reduces the threat of oil entering the Loop Current and affecting the Florida Keys and U.S. East Coast. As I explain in my Loop Current Primer, the Loop Current is an ocean current that transports warm Caribbean water through the Yucatan Channel between Cuba and Mexico. The current flows northward into the Gulf of Mexico, then loops southeastward just south of the Florida Keys (where it is called the Florida Current), and past the western Bahamas. Here, the waters of the Loop Current flow northward along the U.S. coast and become the Gulf Stream. With current speeds of about 0.8 m/s, the Loop Current is one of the fastest currents in the Atlantic Ocean. Every 6 - 11 months, the top bulge of the Loop Current cuts off, forming a 250-mile diameter circular eddy in the middle of the Gulf of Mexico. This clockwise-spinning eddy is filled with warm water from the Loop Current, and is called a Loop Current Eddy. The main body of the Loop Current then takes a fairly direct eastward path from the Yucatan Channel to the Florida Keys.

Over the past two days, surface currents in the Gulf of Mexico have aligned to form a Loop Current Eddy, as seen in the analysis of surface currents done by the U.S. Navy (Figure 1, and see also a 30-day animation of the eddy forming.) It remains to be seen if the deep water currents have followed suit, and a stable Loop Current Eddy cannot exist until the deep water currents also cut off into a clockwise-rotating ring of water at depth. A NOAA Hurricane Hunter aircraft is out over the Gulf of Mexico today dropping expendable buoys and current probes to determine if a stable Loop Current Eddy has formed. Roffer's Ocean Fishing Forecast Service has a nice discussion on the Loop Current Eddy formation.


Figure 1. Comparison of surface currents in the Gulf of Mexico on May 19 (top) and May 27 (bottom) as simulated by the HYCOM model. On May 19, the Loop Current made a large northward loop into the Gulf, and was able to transport oil from the near the spill location southwards through the Keys. By May 27, this loop had cut off, and new oil moving southwards from the spill will now be trapped in the clockwise rotating Loop Current Eddy that is cut off from the Loop Current. Note on the west side of the Gulf of Mexico, off the coast of Texas, there is an old Loop Current Eddy that cut off from the Loop Current in July 2009. This eddy cut off in the same location as this week's eddy, and has drifted west-southwestward at 3 - 5 km per day over the past ten months. Image credit: U.S. Navy.

If the eddy does remain in place, it will greatly reduce the chances of oil making it to Cuba, the Florida Keys, and beyond. Any oil moving southwards from the spill location will now become entrained in the eddy, and will move in a 250 mile-wide clockwise circle in the east-central Gulf of Mexico. A small portion the oil will get shed away from the eddy's periphery and make it into the Loop Current and waters surrounding the eddy, but the concentrations of oil doing so will be small. Keep in mind, though, that during the first 1 - 2 months that a Loop Current Eddy forms, it is common for the eddy to exchange substantial amounts of water with the Loop Current, and in some cases get re-absorbed into the Loop Current. A 1-year animation of the Loop Current shows that the last Loop Current Eddy, which cut off in mid-July 2009, experienced a 2-week period in early August when it re-attached to the Loop Current. A significant portion of any oil entering the eddy during a period of re-attachment will be able to enter the Loop Current and flow past the Keys.

One bad result of the eddy breaking off is that now we have an extra source of heat energy for passing hurricanes during the upcoming hurricane season. Loop Current eddies have high-temperature water that extends to great depth, and hurricanes passing over such eddies often undergo rapid intensification. Hurricanes Katrina and Rita of 2005 both underwent rapid intensification as they passed over warm Loop Current eddies in 2005. The formation of a Loop Current Eddy during hurricane season means that a much greater portion of the Gulf of Mexico has deep, warm water capable of fueling rapid intensification of hurricanes.

Oil spill update
Light offshore northwesterly winds are expected to blow over the northern Gulf of Mexico today through Saturday, resulting decreased threats of oil to the Louisiana shore, according to the latest trajectory forecasts from NOAA. These offshore winds may be able to transport oil southwards into the Loop Current Eddy that just formed; a streamer of oil moving southeastward into the Loop Current Eddy is visible in yesterday's NASA MODIS imagery (Figure 2). Winds will shift to onshore out of the south on Saturday night, then shift to southwesterly by Tuesday. The long-range forecast from the GFS model indicates continued southwesterly winds all of next week. If this forecast verifies, we will see our greatest chances yet of significant amounts of oil reaching the beaches of Mississippi, Alabama, and the Florida Panhandle.


Figure 2. Visible satellite image of the Gulf of Mexico taken at 2:55pm EDT Thursday May 27, 2010, by the MODIS instrument on NASA's Aqua satellite. Thin streaks of oil can be seen moving southeast and then southwest around the eastern side of the new Loop Current Eddy. Image credit: NASA.

Oil spill resources
My post, What a hurricane would do the Deepwater Horizon oil spill
My post Wednesday with answers to some of the common questions I get about the spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
Synthetic Aperture Radar (SAR) imagery from the University of Miami

Central American disturbance
The Atlantic is currently quiet, with none of our reliable global forecast models predicting tropical cyclone development over the next 6 days. There is an area of disturbed weather (90E) just off the Pacific coast of Mexico that will be a major concern for southern Mexico and much of Central America over the next 3 - 4 days. The disturbance will bring heavy rains to Central America during the weekend, potentially bringing serious flooding rains to portions of Mexico, Guatemala, El Salvador, Honduras, and Nicaragua. NHC is giving the disturbance a high (>60% chance) of the disturbance developing into a tropical depression by Sunday. Wunderbloggers Weather456 and StormW have more on the tropics.


Figure 3. Satellite image of the Central American disturbance 90E this morning.

Join the "Hurricane Haven" with Dr. Jeff Masters: a new Internet radio show
Beginning next week, I'll be experimenting with a live 1-hour Internet radio show called "Hurricane Haven." The show will be aired at 4pm EDT on Tuesdays, with the first show June 1. Listeners will be able to call in and ask questions. Some topics I'll cover on the first show:

1) What's going on in the tropics right now
2) Preview of the coming hurricane season
3) How a hurricane might affect the oil spill
4) How the oil spill might affect a hurricane
5) New advancements in hurricane science presented at this month's AMS Conference on Hurricanes and Tropical Meteorology
6) Haiti's vulnerability to a hurricane this season

I hope you can tune in to the broadcast, which will be at http://www.wunderground.com/wxradio/wubroadcast.h tml. If not, the show will be recorded and stored as a podcast.

I'll be back with at least one update over the coming 3-day Memorial Day weekend. Have a great holiday!

Jeff Masters

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1657. xcool



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1656. xcool
yeah crazy ngp
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Quoting SouthALWX:

It's all difficult =P


Some things more so than others, however.
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00Z NOGAPS has some development in 120 hours in the Western Caribbean.
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Quoting KoritheMan:


Yeah, but anticyclones are incredibly difficult to predict.

It's all difficult =P
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Regardless, our immediate concern is the very real potential for life-threatening flash flooding and mudslides across portions of Central America over the next several days. I get the feeling that dozens could die, given the very slow motion of the system.
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1651. xcool
i give a 20% to survive in gom...
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Quoting SouthALWX:

If the anticyclone remains intact, it could regenerate fairly quickly


Yeah, but anticyclones are incredibly difficult to predict.
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Quoting FloridaTigers:


Possible, but if it crosses through the long way, the Yucatan, which imo seems the most likely route, it won't be much except disorganized moisture once it exits. Won't have much time to organize unless it stalls in the Gulf.

If the anticyclone remains intact, it could regenerate fairly quickly
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The only chance of 90E becoming anything even remotely interesting in the Atlantic is if, as SouthALWX said, a piece of energy cuts off from the low- to mid-level vorticity maximum, and into the Caribbean, where vertical shear is gradually becoming more favorable.

Even if that were to occur though, the unseasonably strong mid-oceanic trough would quickly eject it ENE to NE out of the Caribbean, which wouldn't allow for much organization.
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1647. xcool
pictures if Low does survive gom high sst mmmm
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Quoting SouthALWX:

it may or may not. even if the LLC doesnt survive, it may have enough energy to send a piece to the carribean where shear would also be favorable.


Possible, but if it crosses through the long way, the Yucatan, which imo seems the most likely route, it won't be much except disorganized moisture once it exits. Won't have much time to organize unless it stalls in the Gulf.
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1645. xcool
i'm wait to see ,..
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Quoting FloridaTigers:
I just don't see this thing surviving the trek across, especially at this speed.

it may or may not. even if the LLC doesnt survive, it may have enough energy to send a piece to the carribean where shear would also be favorable.
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I just don't see this thing surviving the trek across, especially at this speed.
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http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8shr.html
check out the anticyclone :)
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Chances are this system never gets past 40 kt.
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1640. xcool
nhc wait on new year..
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that may be the actual problem. They dont want to say TD and not know where it will go! This is Agatha. Check out the outflow and dmax is on its way. only issue is land interaction, gotta watch that closely.
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1638. JLPR
Quoting xcool:
5am DEPRESSION


Yep, it should already be TD1-E ¬¬
But when this get named by the NHC we will get our shiny 3 and 5 day track by them ^^
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1637. xcool
yeah big time
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1635. xcool
SouthALWX haha
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90% ... jeeze just call it what it is ... lol they dont want to name it because a TS this early makes their below average epac look bad =P
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1633. xcool
i think need ECMWF Tweaking
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1632. xcool
5am DEPRESSION
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000
ABPZ20 KNHC 290557
TWOEP
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1100 PM PDT FRI MAY 28 2010

FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

RECENT MICROWAVE SCATTEROMETER DATA SHOWS THAT THE CIRCULATION
ASSOCIATED WITH THE LOW PRESSURE AREA CENTERED ABOUT 225 MILES
WEST-SOUTHWEST OF PUERTO DE SAN JOSE GUATEMALA IS BECOMING BETTER
DEFINED. IF CURRENT TRENDS CONTINUE...A TROPICAL DEPRESSION COULD
FORM LATER TODAY AS THE SYSTEM DRIFTS NORTHEASTWARD
. THERE IS A
HIGH CHANCE...90 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS. HEAVY SQUALLS ARE ALREADY
APPROACHING THE COAST OF EASTERN MEXICO AND GUATEMALA AND THE AREA
OF HEAVY RAINS EXTENDS AS FAR EAST AS EL SALVADOR. THESE RAINS ARE
LIKELY TO CONTINUE AND COULD CAUSE LIFE-THREATENING FLASH FLOODS
AND MUD SLIDES IN THESE AREAS OVER THE NEXT COUPLE OF DAYS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER BEVEN
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Quoting JLPR:


Possible, lets see what happens, if it moves as slow as it is moving now as it crosses, it may very well loose its circulation or dissipate, but who knows. XD

completely plausible. most importantly, the ECMWF starts to bring everything very much zonal towards the first week of June.... Summer is here and the STJ is retreating. get ready :)
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lol
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1627. xcool
i cannot stop lmao
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1626. xcool
lol
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1624. JLPR
Quoting SouthALWX:

from what I can tell, it makes Agatha then rips it to pieces over central America. Poof.


Possible, lets see what happens, if it moves as slow as it is moving now as it crosses, it may very well loose its circulation or dissipate, but who knows. XD
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coming from me? thats what the ECMWF says. didnt say I agreed with it.
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Quoting FIU2010:
ok, plz let me know, guys

from what I can tell, it makes Agatha then rips it to pieces over central America. Poof.
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1620. xcool
Link

go here..
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1618. xcool
FREE sites better
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1617. xcool
FIU2010 DID..
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Quoting FIU2010:
but i thoughts the latest ecm already came out, guys? which one are you guys waiting for next?

it is rolling. he is posting the individual images as they are available. it is "out" but not entirely.
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just a few more mins for 00z :DDD
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1613. xcool
FIU2010 WAIT TO SEE OOZ
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Quoting FIU2010:
guys, what is it exactly showing? because i didn't quite understand the run.
12z had 90e cross but waiting for 00z to come out here
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1610. xcool
FIU2010 ON ???
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^ 12z still waiting for 00z data here
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1607. xcool
SouthALWX YEAH.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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