First Atlantic Invest, 90L is here; oil now 350 miles west of Key West
An extratropical low pressure system has developed a few hundred miles northeast of the Bahamas today, and has been designated as the first "Invest" of the year (90L) by the National Hurricane Center. (For those of you who were wondering, a discussion of what an "Invest" is can be found in the Tropical Cyclone FAQ). This low has the potential to develop into the season's first named storm--Alex--and could be a threat to the Southeast U.S. coast by Tuesday. Wind shear is currently 40 knots over the low, and the high shear ripped apart a low level circulation that was attempting to form this morning. Water vapor loops show a large amount of dry, continental air exists to the west of the storm, and this dry air will hamper transition of 90L to a subtropical storm. This system is expected to move slowly northwestward towards the Southeast U.S. coast, and could bring 20 - 30 mph winds and heavy rain to the coast of North Carolina by Tuesday. While the storm will initially form in a region of high wind shear and be entirely extratropical, it will move into a region of lower wind shear in a gap between the polar jet stream to the north and the subtropical jet stream to its south early next week. At that time, the low will be positioned near the warm waters of the Gulf Stream, and will have the opportunity to develop a shallow warm core and transition to a subtropical storm. The models are divided on whether the storm will eventually make landfall on the Southeast U.S. coast 5 - 7 days from now, and it is too early to offer odds on this occurring. The counter-clockwise flow of air around this low will probably lead to northeasterly winds over the oil spill region Tuesday through Wednesday, keeping oil away from the coasts of Alabama and the Florida Panhandle, but pushing oil southwards towards the Loop Current. Wunderbloggers Weather456 and StormW have more detailed discussions of the potential development of 90L.
Figure 1. Visible satellite image of 90L this afternoon.
Potential heavy rainfall threat to Haiti next week
Long-range forecasts from the NOGAPS model, and to a lesser extent, the ECMWF and GFS models, continue to predict an increase in moisture and decrease in wind shear over the Western Caribbean 4 - 6 days from now, leading to development of a tropical disturbance with heavy rains in the Western Caribbean early next week. A strong subtropical jet stream over the southern Gulf of Mexico will steer the disturbance to the north and east, and the potential exists for heavy rains of 2 - 4 inches to affect eastern Cuba, Jamaica, Haiti, and the Dominican Republic in the Wednesday - Thursday time frame next week. The models are less enthusiastic about the prospects for tropical development than they were in yesterday's runs, and it currently appears that high levels of wind shear will make formation of a tropical depression improbable.
Oil spill continues to impact Louisiana shores
Light southeast to east winds are expected to blow over the northern Gulf of Mexico today through Sunday, resulting in potential oiling of Louisiana shorelines from the mouth of the Mississippi River westward 150 miles, according to the latest trajectory forecasts from NOAA. These winds may be creating strong enough surface currents that the flow of oil southwards towards the Loop Current may be significantly reduced or shut off over the next few days, as suggested by the latest SAR satellite imagery (Figure 2). However, winds will shift to offshore out of the north or northeast by Tuesday, due to counter-clockwise flow of air around the approaching 90L storm. If 90L becomes strong and lingers off the Southeast U.S. coast for several days, a significant amount of oil could get pumped into the Loop Current next week.
Figure 2. Synthetic Aperture Radar (SAR) image of the oil spill taken at 11:53pm EDT May 20, 2010, by the European Space Agency's ENVISAT satellite. The plume of oil being drawn south towards the Loop Current appears truncated, and very little oil may be flowing south. Image credit: Center for Southeastern Tropical Advanced Remote Sensing, University of Miami Rosenstiel School of Marine and Atmospheric Science. SAR images have a resolution of 8 - 50 meters, and can be taken through clouds and precipitation.
Oil now 350 miles due west of Key West
Satellite imagery from today's 12:15pm EDT pass of NASA's Terra satellite (Figure 3) shows that a narrow ribbon of oil is caught in the Loop Current. The oil has moved south and then southwest, and the leading edge of the oil is now about 350 miles due west of Key West, Florida. The oil is substantial enough to modify the cumulus clouds in the Gulf of Mexico, though NOAA characterizes this portion of the oil spill as "numerous light sheens with some emulsified patties and streams." The oil is now headed away from the Keys towards a major kink in the Loop Current. By Saturday, the oil should double back towards the Keys in a eastward flowing branch of the Loop Current, and will likely pass just south of Key West by Tuesday. However, this is not a sure thing. As I discussed in my post Wednesday, the Loop Current is very unstable right now, and is ready to cut off into a giant clockwise-rotating eddy, an event that occurs every 6 - 11 months. This event could occur today or tomorrow, in which case the ribbon of southwestward-moving oil would turn due west and then north, eventually winding up back near the site of the Deepwater Horizon blowout. Roffer's Ocean Fishing Forecast Service has a nice discussion on the possibility of the Loop Current cutting off into a Loop Current Eddy. Keep in mind, though, that during the first month that a Loop Current Eddy forms, it exchanges a considerable amount of water with the Loop Current. Even if a Loop Current Eddy forms today, I still expect we will see some oil make the turn eastward and flow past the Florida Keys by Wednesday.
Figure 3. Visible satellite image from NASA's MODIS instrument for 12:15pm EDT May 21, 2010. I've enhanced the region along the eastern boundary of the Loop Current showing the south and southwestward moving ribbon of oil. Note that the oil is substantial enough to be affecting the low level cumulus clouds along portions of the ribbon of oil. The oil has reached the latitude of the Florida Keys.
Oil spill resources
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
I'll be back with a new post Saturday afternoon.
Jeff Masters
Reader Comments
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If you're talking about diurnal changes in convection intensity, they exist everywhere in the tropics where warm water supports convection. However, 90L will not be affected much because any convection associated with it is not being generated by the low itself, but by the shortwave trough above it. It isn't tropical and thus isn't self-sustaining yet. There may be some effect in the surface-based instability, but not little overall effect on the convection associated with 90L.
That in my opinion is the strongest swirl, in subtropical systems the CoC can be very far off from the convection, and naturally I see the greatest spinning coming from this area. Not to mention that the NHC considers this to be where the lowest pressure is.
GOES-East IR Imagery Loop - Atlantic Basin
Wow that's way back there....that'll likely take a big jump east in the morning once those swirls dissipate. Perhaps even by 6z.
diurnal cycles, in some form, affect everywhere.
I cannot see any Northwest movement with 90L, now or in the next 2-3 days.
I am seeing ENE, then E. And discontinuation of its # around Sat night Sun morning.
Cant see what will be so strong as to change this .
yeah, if we're going by dying swirls, give me ten minutes and I'll have several coordinates =P
The big big thing to remember is that 90L is not tropical, it is extratropical right now. Its designation makes us want to analyze it like a tropical system but it simply isn't yet. It is being supported by the shortwave aloft and that's all. Without the shortwave it would die. You are right in that it will drift ENE over the next day or two and then get pulled north when the trough-split occurs off the eastern seaboard late this weekend.
From there the upper cut-off low will adopt the surface circulation and bring it westward underneath. At this point the low will start to become warm-core, and thus subtropical. That is when things will get really interesting. For now, it's like any other nontropical low that gets stuck in the subtropical latitudes with not much place to go. The surface low will keep jumping eastward trying to follow the upper shortwave while fighting the easterly surface winds trying to pull it westward, like we're seeing with those swirls.
I actually agree with that location its pretty close to my own guesstimate. I suspect either the CoC will begin to relocate overnightm or the moisture itself might start to spin around towards it. The whole thing is very interesting though.
The COC will keep trying to form under the western edge of the convection, but will likely get exposed a couple more times due to westerly shear. The system is fairly certain to curve back north and eventually west as the trough-split off the eastern seaboard "attracts 90L towards itself.
The focal point of arc clouds which is a center fix technique is 26N/69.5W. The center is broad and may contain multiple vortices.
Ah we will. The low just has to reform under the area of upper divergence associated with the shortwave. It's about to "jump", and may already have.
You're missing the big picture. We knew it would disspate .. shear and upper convergence/ subsidence will do that. read Levi's post above.
AOI
AOI
AOI
AOI
Aaahhh! OK. I see the problem I am having.
Will keep monitoring it then. You expect the convection to catch up with the location that the Navy just issued? Or will the COC perhaps relocate?
All the center seems to be following what we here are seeing.
The center will keep trying to "jump" back under the area of upper divergence that is supporting it, which is where the convection is. It will likely keep reforming under the western edge of the convection but the shear and easterly surface winds will keep trying to push it out and expose it, like the current naked swirls. The low may have already jumped east, but if it has it is still broad and may have multiple vortices like 456 was saying. Tomorrow morning should see the official center position shift greatly to the east.
Yeah, I see that Dudus is causing probs.
Talking about hot, hot, hot, elections here on Monday. We may get our first Woman Prime Minister, seems to me.
?
Have a fine evening.
sussea what now?
Till 2mr.
BP is sticking with its dispersant choice
What a bunch of clowns!!
Why, you need to be smacked again?
What did you do this time?
BTW, its not a stick... its a Cricket thingy.
Ah yes! The saga continues. We're living the soap opera. The rumor mill is working overtime and they get more ridiculous by the minute.
Hopefully your elections will be calm and uneventful, please don't follow our bad behaviour!!!
Send the rain!!! We need to cool down!!!
A due west course would take the system right into South Florida
Just watch out for the Googly's :)
that would be a mallet lol
I think sussenered is sheared, and oytonere means outer part
Tropical Cyclone Advisory NUMBER NINETEEN
CYCLONIC STORM BANDU (ARB01-2010)
5:30 AM IST May 22 2010
=======================================
At 0:00 AM UTC, Cyclonic Storm Bandu over west central Arabian Sea and adjoining Gulf of Aden further moved westward and lays centered near 12.5N 50.5E, or about 70 kms north of Alula, Somalia.
The dvorak intensity of the system is T2.5. The 3 minute sustained winds near the center is 40 knots with a central pressure of 994 hPa. The state of the sea is high around the system's center. It has tracked westward with the speed of 4 knots during the past 12 hours.
The system is associated with curved band pattern. Broken intense to very intense convection is seen over west central Arabian Sea between 10.5 to 13.5N and between 50.0E to 54.0E in association with the system. Cloud top temperature due to convection is -65 to -70C.
The upper level steering winds in association with anticyclonic circulation to the north northeast of the system are favorable for west northwest movement of the system over the Gulf of Aden.
Vertical wind shear is moderate, the low vorticity, convergence, and upper level divergence suggest the system will maintain the same intensity for some time. Subsequently, an increase in vertical wind shear along with the entrainment of drier air from the adjoining land areas, cooler sea surface temperature over the Gulf of Aden, and interaction with land surface is expected to gradually weaken the system.
Forecast and Intensity
========================
24 HRS: 13.0N 49.5E - 35 knots (Cyclonic Storm)
48 HRS: 13.5N 48.5E - 25 knots (Depresion)
I am having a tough day with words today..
Apparently... SWMBO wants me to go to the Victoria Highland Games on Sunday.
Not totally sure what it is... but it seems to be based on men wearing skirts and little furry purses... and playing with sticks and rocks??
Indeed. I believe my estimate was inline with yours. Ive noticed that the midlevel turning is especially evident in 90L preceding a center relocation. the turning veers just prior to the relocation. Shortwave IR verifies that idea. may be useul in the future as it may be indicative if exactly where and what intensity the shear is with 90L
Ok, now that makes sense :)
P.S. And drinking some kind of alcohol that has to be mixed with copious amounts of root beer just to get over the Smell & Taste.
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