cieldumort
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Here is a nice mid-day, "Visible" look at Invest 92L, which was drifting northeast near the Azores on June 1, 2009, the official start of the 2009 Atlantic Hurricane Season. (Click "Attachment" to view)
The most recent QUIKSCAT pass shows a large area of 30 knot winds within the reasonably symmetrical cyclone. (Time sensitive)
92L is starting to pass over progressively cooler waters, and has been trending less and less spherical. Nonetheless, current estimates are that 92L is down around 1001mb with maximum sustained winds of about 35 knots, per Navy guidance, and per has a "Low" chance of becoming a subtropical storm.
A neat, little, not-so-little feature, kicking off Day 1.
More information on 92L is available from here.
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MichaelA
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It is an interesting feature. With the large cyclonic field, it appears to be more of a mid-lat/mid-Atlantic storm. It's very far North and over relatively cool waters. I agree that there is only a tiny potential for either subtropical or tropical development.
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Michael
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cieldumort
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The feature which is now Invest 92L has become much better organized than 36-48 hours ago, and has clearly been taking on progressively more and more classic tropical characteristics, even at its relatively high latitude and while over cooler waters.
Invest 92L is looking more and more like one of those high seas subtropical-tropical hybrids that occasionally make it into the record books with a name.
Here are some of the latest classifications of 92L from SSD:
DATE/TIME LAT LON CLASSIFICATION STORM
02/1800 UTC 44.0N 24.1W ST3.0 92L
02/1200 UTC 42.7N 23.8W ST3.0 92L
02/0600 UTC 41.7N 23.8W ST2.5 92L
01/2345 UTC 40.7N 23.9W ST2.5 INVEST
01/1745 UTC 39.9N 24.7W ST1.5 INVEST
And the latest estimated range from AMSU:
INVEST 92L
Tuesday 02jun09 Time: 0714 UTC
Latitude: 42.49 Longitude: -23.59
Storm position corresponds to AMSU-A FOV 27 [1<--->30]
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| Estimated MSLP: 984 hPa
| Estimated Maximum Sustained Wind: 55 kts
| Estimate Confidence: Fair ( +/- 10mb +/- 12kts )
As of 2PM EDT, estimates of intensity and wind speed so far today are in a wide range from about 972-996mb, with maximum sustained wind estimates of between roughly 40 and 75 mph.
I have read speculation that it appears that there may be some hesitation to forecast more liberally on 92L than what might otherwise be expected given its impressive structure, in some part, because of the proximity to RSMC La Réunion-Tropical Cyclone Centre/Météo-France, but I have no knowledge of the legitimacy of such a claim.
Time-sensitive Visible Loop of 92L
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danielw
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Interesting indeed. Here's the latest Tropical Model text output from 18Z today. 2PM EDT
TROPICAL CYCLONE GUIDANCE MESSAGE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1827 UTC TUE JUN 2 2009
DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.
PLEASE REFER TO OFFICIAL FORECASTS FOR TROPICAL CYCLONE
AND SUBTROPICAL CYCLONE INFORMATION.
ATLANTIC OBJECTIVE AIDS FOR
DISTURBANCE INVEST (AL922009) 20090602 1800 UTC...
...INITIAL CONDITIONS...
LATCUR = 44.0N LONCUR = 23.8W DIRCUR = 355DEG SPDCUR = 11KT
LATM12 = 41.7N LONM12 = 23.7W DIRM12 = 10DEG SPDM12 = 10KT
LATM24 = 40.1N LONM24 = 24.7W
WNDCUR = 45KT RMAXWD = 30NM WNDM12 = 40KT
CENPRS = 995MB OUTPRS = 1012MB OUTRAD = 300NM SDEPTH = D
RD34NE = 60NM RD34SE = 60NM RD34SW = 0NM RD34NW = 0NM
Current estimated winds of 45kt and pressure of 995mb would indicate that the system is probably a hybrid system. Subtropical with tropical characteristics.
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MichaelA
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It looks like it's doing a little loop this morning. Still not very tropical in appearance with limited convection near the CoC. It could be a rather nasty storm if it makes landfall in France or England.
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Michael
PWS
Edited by MichaelA (Wed Jun 03 2009 08:09 AM)
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cieldumort
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Invest 92L has essentially been absorbed by the larger upper-level trough with which it has been dancing for several days, and never really developed sustained, deep convection, typical of most bona fide tropical cyclones. has stopped featuring the system in its discussions, the floater previously over 92L has been dropped, and it looks as if that is that.
For a duration of about 48 hours, 92L did develop numerous showers and thunderstorms within fairly tight bands over and near its coc, with two belts of maximum sustained winds: one closest to the coc, more typical of tropical cyclones, and another about mid-way out, more typical of subtropical cyclones.
It appears that there were two primary detractions keeping 92L from getting a name: 1) A relative inability for the convection, while appropriately-placed, to get very deep, and 2) A relative inability for 92L to sufficiently free itself from the grasps of its parent extra-tropcial cyclone, which ultimately may have been its undoing.
Almost certainly one of the most impressive higher-lat subtropical/tropical-ish hybrid systems we see. Not a Vince or Epsilon, but it held its own for the better part of 2-3 days.
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CoconutCandy
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Good, insightful discussions, as usual.
Yep. It appears that insufficient thunderstorms (quantity and strength) conspired to keep this little invest out of the record books. Actually, we can blame it on the insufficient SST's.
More than most people realize, other things being equal, the intensity and depth of oceanic thunderstorms is closely correlated with the temperature of the underlying sea surface.
When I found that the SST's near 92L were far too cold, I knew the likelihood of true (pure) tropical cyclogenesis was nearly nonexistant.
It really does take SST's of nearly 80 F (27 C) to have enough 'vapor pressure' to produce the 'kind' of thunderstorms (very rich in moisture), which, when sufficiently organized, can release enough 'latent heat of condensation' over a large-enough area and over a long-enough time span to actually WARM the middle layers of the atmosphere sufficiently enough for significant mid-level pressure falls to occur.
And the whole system, through a 'positive convective-feedback mechanism' (more, stronger, deeper and even better organized thunderstorms) continue until surface pressures head south of the border. Eventually, the converging, cyclonic windfield strengthens (because of the lowering central pressures and a 'tightening' pressure gradient) to the crucial threshhold of 30 Knots and Viola! A depression is born. Thanks, essentially, to a bunch of VERY intense thunderstorms acting in concert over a large enough area and over a long enough time scale to generate a self-sustaining warm core. Tropical cyclogenesis in a nutshell.
(Please realize that the above 2 paragraphs do not apply to 92L, as it was already a well-developed cyclone of NON-tropical origins, and already had a well-established cyclonic wind field of tropical-storm-strength, BUT resulting from 'baroclinic' (cold core) 'extratropical' processes.)
Bottom line: To acheive Tropical Depression (true warm-core cyclone) status requires a LOT of sufficiently deep and strong thunderstoms to impart a sufficient amount of 'latent heat' to the mid-atmosphere to begin lowering pressures and get the whole thing started.
And only SST's of at least (around) 80F can produce copious amounts these types of deep and extremely moist thunderstorms. We're not talking your average, garden-variety thunderstorm. These are truely the tropics' "hot towers", for the amount of heat they release into the middle and upper layers of the atmosphere, with cloud tops colder than -80 C and 'convective turret penetrations' well into the stratosphere, at more than 60,000 feet!
Ultimately, it was the laws of physics (vapor-pressure temperatures of the sea surface water), that precluded the possibility of the type of sustained, deep thunderstorm activity needed to establish that all-essential warm core.
Although 92L certainly had strong enough winds and low enough central pressure to qualify as "Tropical Storm Force", but it never quite acquired the *essential warm core* required to qualify as a tropical system. Not with those sniggling SST's.
Moral of the story: Appearances can be deceiving. We've all watched many non-tropical systems which "look" quite striking, even hurricane-like, even sometimes with an eye-like feature. But an impressive-looking swirl of clouds is *sometimes* just that. yes, but decidedly not the same animal as a TC or Sub-TC, despite appearances.
One should look into the thermodynamic processes occuring in the mid-levels of the low, to determine if a warm-core transition is occuring (or not), or even likely to occur (or not), based on the degree/extent/moisture content/depth/organization of the thunderstorms, which in turn, are 'based' on the underlying SST's.
Take away: Vapor Pressure Temperature increases *dramatically* around 80F, so the air can hold *much more* water vapor, the very fuel needed to spawn and sustain true tropical cyclones.
Ah, that essential 27 C isotherm. The Encroaching 27 C Isotherm Coming soon to a coastline near you.
So, you may ask: What's in a name? A Warm Core! (Or sometimes neutral. See below post!)
Edited by CoconutCandy (Fri Jun 05 2009 11:02 AM)
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cieldumort
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A great follow-up from CC above. A few of those observations probably can do with a little extra information, so as not to leave anyone with more confusion than such a thread is already bound to create 
Contrary to what CC may have seemed to imply, temperatures of at least 27C (80F) are not always a necessary ingredient to cook up a warm core. Depending on the temperature of the atmosphere above, and other factors, tropical cyclogenesis can, and often does, occur, in regions where water temps are running considerably below the oft-cited 27C.
The most recent example of this was just last week, as TD-1 formed over water temps that were averaging about 25-26C.
To digress a moment while on the topic of 2009's TD-1, here's a little bit of tropical cyclone trivia that might be of interest: Last week's TD was actually the farthest north any official preseason tropical or subtropical cyclone has ever formed in the Atlantic basin!
Another point of clarification worth noting - While by very definition Tropical Cyclones are warm-cored systems, Subtropical Cyclones can be either neutral, or warm core. Given that 92L was generally neutral, with some hints of an incipient warm core trying to become established with the aid of some warm seclusion that had already taken place, it is probably not unreasonable to refer to it as a bona fide subtropical cyclone, despite not being named.
There has been some research that strongly suggests that there are actually far more subtropical cyclones than have been named. Generally speaking, those subtropical cyclones that actually do get a name, or that get added posthumously as a hurricane season "storm," either have a more 'classic' structure to them than usually the case.. as these are hybrids, it is not surprising then that some are only added after the fact, having been extensively reviewed in the post-season, and found to have been sufficiently developed for the post-season upgrade. A recent example of this is the '2005 Unnamed Subtropical Storm' (PDF), which was thought to be mostly extra-tropical, until more thorough examination of the system determined it to qualify for inclusion in the 2005 Atlantic hurricane season record books.
Finally, and as this can add extra 'fuel' to many another fire, we won't discuss the how and why of it, the trends of recent decades are for the tropics, and thus warmer SSTs, to be expanding ever poleward. In addition, air and SST temps are also already increasing fastest in the higher latitudes, as it is. Whatever the cause of this trend, an obvious consequence of these ever-expanding warmer waters, is a greater percentage of the earth being covered in SSTs that are more and more supportive of tropical and subtropical cyclogenesis... certainly an interesting development for those of us that track these storms.
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CoconutCandy
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Thank you for 'setting the record straight' with regard to SST's.
Quote:
... temperatures of at least 27C (80F) are not always a necessary ingredient to cook up a warm core. Depending on the temperature of the atmosphere above, and other factors, tropical cyclogenesis can, and often does, occur, in regions where water temps are running considerably below the oft-cited 27C.
The most recent example of this was just last week, as TD-1 formed over water temps that were averaging about 25-26C.
Entirely correct. My discussion above was a bit too over-simplified, focusing solely on SST's, thunderstorm *intensity* and the vapor pressure temperatures necessary to impart the degree of energy (latent heat of condensation) requisite to cause substantial warming of the mid-levels and resultant pressure falls.
Usually, *all other factors being equal*, it takes SST's of about 26C to trigger this series of events. (Technically, it is the saturation vapor pressure of the ascending air parcels within the thunderstorms, and the *increasingly huge amount* of latent heat they carry upwards, once SST's attain that seemingly 'crucial degree' of warming and to a sufficient depth.)
Obviously, many factors come into play: Upper-level divergence, lack of appreciable shear, the lapse rate throughout the depth of the entire atmosphere, the measure of the 'convectively available potential energy' (CAPE), various stability indexes, the amount of 'precipitable water' in the area, and many other factors, can and do 'offset' the effects of the less-than-desirable SST's, especially when one includes the occurances of sub-tropical systems into the scope of consideration.
Clearly, I need to learn more (love to learn!) about the nature of neutral-core systems, especially the thermodynamics involved in subtropical development (transitioning).
In Hawaii, they are called "Kona Storms" and are assigned a Hawaiian name. I think one occurred sometime in the 70's in the month of April (ENSO year?). Will re-search that and post it under "Hurricane Ask/Tell" when I find it.
Finally, I've noticed, too, the large temperature 'anomalies' (2 to 3 degrees!) at high latitude, both in the atlantic and the pacific, over the past few years, and wondered how that might effect the frequency and location of tropical and (especially) subtropical systems in the years and decades to come. Interesting times.
Something is definitely afoot. Global Warming? Say it ain't so!
Edited by CoconutCandy (Fri Jun 05 2009 11:14 AM)
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hogrunr
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I was just looking at a couple of the long range forecasts from Florida State and a couple of them are starting to show a disturbance that develops into some kind of tropical cyclone just East of the Yucatan at about the 96 hour mark (4 days out)...wanted to get some other opinions on this and if you see anything besides these models to support this?
As the models take it on out, they have it headed up across Cuba and close to Florida.
http://moe.met.fsu.edu/tcgengifs/
Specifically the and models.
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