09/06/05 FCST: Hurricane Ophelia

[Dustin Wilcox]

By no means am I an expert on Tropical Systems but as far as I can tell it looks as of 12:30 PM the system is becoming much more organized with a large flare up of convection that now appears to be wrapped around the center, I wouldnt be suprised to see some slight pressure falls through this evening.

 

[Dustin Wilcox]

Winds are up to 65mph in latest advisory there is also now mention of the system becoming a Hurricane in the next 24 hours.

 

[Jeff Snyder]

Cold water upwelling may become an issue, but I believe there is a significant threat of dry air entrainment. A look at the water vapor imagery loop shows very dry air pressing into Ophelia from the north and northwest. So far, O has fought it off, but it wouldn't take much for that dry air to get wrapped into the circulation. Dry air is also trying to press in from the south and southeast. We've all seen how dry air can weaken a storm, and I wouldn't be too surprised should this happen to Ophelia.

 

[Mike Hollingshead]

Latest GFS strengthening this into a major hurricane and taking it up the east coast. The GFS did very well with Katrina but also recently had a strong cane vanish a run later. As slow as it moves it I would agree with Jeff that upwelling would seem a certain problem. I hope we don't have any cities below sea level over there. :shock:

 

[HAltschule]

Interestingly, several 12z models now do the "hook and loop" technique and bring the big O inland as a major hurricane. There are big differences in track still (as one might imagine)...ranging from Savannah, GA to Hatteras, NC.

EDIT: 5pm: Ophelia Upgraded to Hurricane with 75 mph. They also have the new official NHC track doing the loop-dee-doop through 120 hours.

 

[Dustin Wilcox]

I am not real sure on the exact effect and process of up-welling, I was curious as to the effect the gulf stream has in the upwelling process. Does the gulf stream decrease the effects since it is constantly flowing thus moving the up-welled water out and replace it with warm gulf stream water?

 

[Mikey Gribble]

I don't mean to get off topic, but I did a search on the gulf stream and came up with this
http://oceancurrents.rsmas.miami.edu/atlan...ulf-stream.html
It says that the gulf stream flow can exceed 5kts at its core, which is about 100-200km wide. It looks like at this time of year, Ophelia would be located near the entrance region to the stronger flow of the gulf stream. I would assume this would mean that the current, in the neighborhood of Ophelia,would average about 3-4kts from the SW. I am sure that the winds from the hurricane have a significant impact on the ocean currents in its immediate vacinity, so it is hard to know how much upwelling would be affected, if at all, by the gulf stream.

 

[HAltschule]

Upwelling of water over that area will have the same cause and effect as in other places. When upwelling occurs, the warm water on top is displaced and the "colder" water from deeper down is brought up in its place. So, despite their being the presence of the Gulf Stream with warmer water on the surface, there will still be "cooler" water brought up from the bottom of the ocean because the water near the surface is heated more. The water deeper down does not receive as much, if any, sunlight and as a result doesn't warm up as much. The upwelled cooler water is not as conducive for strengthening tropical systems. I hope this helps a little?

 

[David Wolfson]

I think upwelling is less of a factor in the Gulf Stream. First, it's relatively deep and, second, it's flow acts like a conveyor bringing unmixed water into the storm circulation. The current NHC discussion mentions the possibility of upwelling if O. moves off the Gulf Stream.

 

[Jason A.C. Brock]

I think it may have been less of a factor due to being on the Gulf Stream but upwelling does occur. Case in point Ophelia is not a Tropical storm at the 4am advisory. I think she will get back to Hurricane strength especailly if she actually starts to move. It will be interesting to see where this thing goes. If the Trough over the plains can move 180-200 miles more East over the weekend it could hopefully push this thing out to sea towards where Maria and Nate ave been hanging out. Im surprised Maria is not Extratropical by now....must be the warm Gulf Stream feeding her. ;-)

 

[HAltschule]

OPHELIA MAY HAVE REMAINED STATIONARY LONG ENOUGH TO BRING UP COOLER WATERS EVEN OVER THE GULF STREAM.

This from this morning 5:00 AM NHC update. It ties in to our discussion as to why Ophelia has not been strengthening too much over the past few days while remaining stationary. Now that she's on the move, albeit slowly, there may be an opportunity for some slow strengthening. On a side note, I'm not sure I have ever seen a more confusing NHC forecast track for a Hurricane than the one at 5am. It is quite confusing and one has to focus on which points are when and what is where. Yeah...exactly, confusing. :roll:

 

[Jeff Snyder]

That water vapor loop is pretty impressive. The dry air to the north-northwest of Hurricane O is pressing HARD into the storm. Cloud tops are recently warmed quite significantly. I can't imagine that dry air won't cause big problems for Ophelia. Waters are pretty warm, and shear isn't too strong, but that dry air slamming into the hurricane is pretty impressive.

 

[Scott Olson]

Latest IR/WV show significant drop off of convection and serious problems with dry air entrainment. Dvorak anaylsis still shows 65+kts but latest Vortex shows 60kt winds at the surface which is below Hurricane force. Lots of uncertainities exist with intensity but it appears Ophelia has increased forward speed and may be heading for the Carolinas with the BAM models farther north. I would expect the NW turn to be a little more imperfect so the GFDL solution is a bit far south near the GA/SC border. GFS is the outlier but many uncertainies remain and the past track versus forecast track looks like a mess. GFDL develops Opehila into a major Hurricane prior to landfall with the FSU in a more reasonable CAT 2 range. With so much dry air and shallower waters im skeptical at the GFDL intensity forecast.

 

[Jeff Snyder]

This goes to show why you can't always evacuate a city with confidence even for a storm so close to land (in the case that Ophelia was stronger, that is). The models have performed badly with Ophelia so far, though the magnitude of error isn't too large owing to the slow motion. Regardless, models are still quite spread, though this isn't as important as the fact that the storm continues to defy most model forecasts. As an interesting note, from my observations, the GFDL, which handled Katrina very well, is performing very poorly with Ophelia. While recent motion has been nearly stationary, it doesn't appear as though Ophelia will recurve into GA/SC as much as models forecasted just 24 hours ago. Now, most guidance brings the storm into eastern NC, though an equal number continue moving the storm northeastward and don't bring Ophelia onto land at all.

It appears that the heart of the dry air aloft is now west-southwest of Ophelia. Many upper-air soundings in throughout the southeastern US have shown extremely dry air in the mid and upper levels the past 2-3 days, which dewpoint depressions on the order of 40-50 degrees C in some locations. This has largely eroded most of the western semicircle of convection. The increased evaporational cooling from such dry air probably hasn't helped much either. Of course, the evident upwelling has resulted in considerably colder SSTs near Ophelia, which is also inhibiting any strengthening. LOL, so between the relatively cool SSTs and the continued dry air slamming into Ophelia, I can't imagine Ophelia will be much more Cat 1 at landfall.

EDIT: Forgot to mention moderate shear over the storm... LOL, between upwelling, dry air entrainment, and moderate shear, she's not in a pretty environment, that's for sure.

 

[HAltschule]

15z Sunday: Appears that dry air entrainment has ceased based on H2O Vapor Loop. Banding features and hints of a decent eye wall appear to be forming from the satellite pictures I have seen. As the NHC states, upwelling will likely limit the amount of strengthening that is possible...especially since she is stationary once again.

Models: Interesting to note that most models and trending toward keeping Ophelia offshore of North Carolina, near the coast and not moving her inland very much. In fact, several of the models keep Ophelia stationary with a northward movement later in the period. It looks to be a race between Ophelia's Northward motion and a trof advancing from the west. If the models are right and contune to trend northward, there may be some threat to NJ, NYC, LI and especially Cape Cod, Eastern MA from Ophelia. Something interesting to watch indeed.