| typhoon_tip |
| (Meteorologist) |
| Sun Oct 16 2005 04:33 PM |
Re: wilma on the way
|
Quote:
First off, I can't see every post on here all the time, so I don't always know if something has already been addressed. Having said that, there is absolutely no statistical discrepancy between the two products.
The HHC product is one based off of simple thermodynamical principles relating temperature to energy content. If you take the temperature over an oceanic depth (100m) and convert it to an energy using those equations, you can obtain the HHC product. Substantial values generally arise for SSTs >27C; non-zero values arise for SSTs >= 26C. I have the two plots up on my browser right now -- the only area where you may see a discrepancy is near the 26C isotherm on the edges, and that is solely because of the color scale used that has all HHC values from about 0-2 kcal/cm^2 as the same color. Those waters drop off in temperature fast below the surface and you'd expect the contributions to the HHC to be near-zero.
I'm not sure what you mean by there being no systems in the western or SW Atlantic this season to churn up the waters...Ophelia did a number on the Gulf Stream waters not all that long ago and the area near and just south/southwest of Bermuda all the way to Florida has seen many, many storms this season -- Tammy, Rita, Katrina, Nate, the aforementioned Ophelia, Irene, Franklin, and Harvey. The near-shore waters -- between the shore and the Gulf stream -- are also going to be cooler than you might expect due to Ekman-related divergence of the waters away from the SE US coast.
Finally, that product is limited in that it doesn't really account for cases like Vince -- the extratropical-subtropical-tropical conversion cases over typically sub-standard SSTs/atmospheric conditions. The only one that really does is MPI, and that doesn't account for shear at all and is generally an overestimator of a storm's actual intensity by 20mb or greater. There is no single product and all of them should be used in concert with each other to balance out their weaknesses. However, for a case in the NW Caribbean such as future-Wilma, it is a pretty useful product to show the energy available to the system. Unlike in the Atlantic, these waters have not been tapped since July with Dennis and Emily.
Simply put, there is no perfect utility to use -- and as I and others have always said, they are just that, utilities. For a storm in the tropics, they work reasonably well. In the subtropics, not as well.
And trust me, I know the differences between all of the types of storms and what they can/cannot do...and I also know that model representation of tropical cyclones AND extratropical transition often borders on pathetic. Intensity forecasting is not an exact science.
As for the climate indices...color me unconvinced. They are more reflections of what is actually occurring as opposed to indicators of what is to come (other than those such as ENSO). The NAO is derived from projecting surface pressures onto rotated EOFs across the northern hemisphere, with different modes from the EOFs proving to be more important than others during particular times of the year. The leading mode only accounts for about 20% of the variance in the entire data set. It's good to know, but once again -- just a utility, not a robust forecast product. And, ultimately, for extratropical transition, we're finding that patterns more consistant with the Arctic oscillation may be more important than the NAO...again though, it's still in the formative stages and only just a utility.
Hi Clark... None of what you said is incorrect.. It's all reasonable to me... Just 4 small points:
First, what I was just touching on with HankFrank is that these numbers are less important as better understanding about the spectra of possible storms is becoming better understood. (I sense we are in agreement here). Events such as Vince, Brazil last April, maybe the Perfect Storm and so forth, they all demonstrate that 26C vs. 27C are not limitations; perhaps looked on with too much rigidity sometimes? Those plots in question, they do have usefulness - that's not even open to debate for obvious reason. It is, however, important to point out that 0 energy is indeed a bit of a misnomer; that is, when we acknowledge the former reasoning. I would just like to add, unless the ocean is frozen over with ice there is always potential energy; it's really a matter of the vertical profile of your troposphere that dictates whether it is usable energy or not... It just so happens that planetary mean tropospheric values favor the end of the spectrum over 80F. It is of course obvious that 90% of systems need the warmer SST, indeed. Having said all that, please elaborate on "The only one that really does is MPI"... I've never heard of such a tool - sounds fascinating.. Is there an availability to the public?
Secondly, the area of the Atlantic that I was referring to when the discussion got under way (....ah, late last night when I was probably to tired to be lucid about the subject matter...my apologies) was the region bounded by 25N and 33N, and between 60W/75W. That area in particular looked at first glance to be a dubiously characterized based on the two urls when in comparison. But, if you go back across the logs I did concede once I saw a decent enough presentation. I agree that Ophelia traversed the area of the Gulf Stream on the western fringe of said area, but, that is not necessarily "in" the said area. Also, the Gulf Stream (as you know) is not a stationary entity... Check this, but I think it moves along at 3kts average? Anyway, that being the case, a month at 3kts, combined with last weeks full latitude southerly flow over that area (as also evidenced by ir anyway) suggests that any processing by Ophelia is pretty much negligible and/or indistinguishable at this time. You are correct that a couple of predators really stalked Florida from the east, but they originated in an area beneath 27 or so N, by more than 65W, making them irrelevant to said bounded area above. As far as Katrina, Rita and on and on...Sure, I have no issue with what they did to any SST's outside the area in question. Though it is too late in the season to expect this, if a system developed and moved N of the Islands and stayed 200naut miles N of Puerto Rico, and curved N near 72W by 25N, it would in fact be traversing an area that has not been processed, or has not been processed in so long that it wouldn't matter... (stated just as a facsimile). Now, that does not discount the possibility that the warm water that is evidenced there may be shallow - I'm fine with integrating for depth.
Thirdly, NAO is defined as a climate index, not doubt...However, it is factually evident that a negative NAO is strongly statistically correlated to a negative anomaly in the Ohio Valley area... And, the NAO has a very short none-linear periodicity that flips phases sometimes weekly in more chaotic times; and, sometimes these changes are almost immediately impacting the westerlies above 30N. The only reason that point was brought up is because (as you know) there is at least "hints" in a lot of the runs that Wilma (should she be named) may get hung up in one such trough... The is particularly evident in the 06z run of the GFS (if you haven't already seen)... There's a lot at stake with that. We have a water -logged New England area that is, for lack of better words...categorically opposed to the notion of a strong tropical or hybrid transitioning system careening at them from the S... Also, obviously the stakes are high in the upper Gulf Coastal region... Point being, all this vulnerability is exposing when the NAO is negative and in tandem, the models just happen to have a teleconnected mid-latitude trough willing to do the steering.
Lastly, I hope no one's knowledge was ever in question... If you ever felt as though that was being questioned, feel free to disregard any of those comments, particularly by me, because I try to go out of my way to consider everyone's point of view.
Can't wait to see what the 12z runs do with this thing...