cycloneye wrote:Re: the previous discussion about some folks not "wanting" development... Maybe there are some, but there are also some that always "want" development. The fact of the matter is that, as has been mentioned previously, only a fraction of INVESTs become tropical cyclones. Many pro mets value their FAR (False alarm ratio), which means that many don't want to forecast a cyclone when one doesn't develop. So, they call them as they see them. It seems that some folks don't like this -- they want us all to be like JB and always mention the "possibility" of development. Sure, he may call some storms well, but how many times does he mention development only to not see any development? I'm not slamming JB, but let's all remember that tropical cyclone forecasting is extremely difficult, particularly cyclone genesis.
How many INVESTs have we had this year? How many posts contain nothing but "Wow, I bet this one will be Beryl!"? I think it's good that Storm2k mods are trying to increase the signal-to-noise ratio, but it's never bad to post a reminder of the golden rule of maintaining high quality -- before you post, ask yourself if others will benefit from your post. If you think they will, then post away. If you think they won't, use the Private Message system. It's just now July 1st, and we've had how many threads about non-cyclones? There've been thousands of posts about convective areas that aren't even tropical depressions... I'm not saying we shouldn't discuss these, but it's tough (and time consuming) to weed through all the one-liner and emoticon-only posts to get to the substance.
That followed some incredibly informative posts about cyclogenesis (formation of a tropical cyclone from merely disturbed weather) and forecasting.
first from wxman57:
I don't look for surface winds to steer such disturbances. Look aloft, probably in the mid levels. Though the surface front may be weak, the disturbance is near the western periphery of the 700mb and 500mb ridge. As such, a track to the north is most likely. The trof (aloft) axis is right along the east U.S. coast, perhaps just offshore. That position isn't going to change much over the next few days, so the chances are that this disturbance will stay off the east U.S. coast then turn NE and out to sea are good. Another trof reaches the east U.S. coat on Sunday, too.
and another post:
Alberto was in a VERY good environment for development. It was parked over an UL anticyclone for several days, and had model support for development for quite some time. Sure, it moved away from the good environment, into a bad environment, but not before it developed.
All these Invests are developing in a completely different environment. No model has been showing any type of development for quite some time now. Strong westerlies continue to dominate the Atlantic. This has been providing sufficient UL divergence for several "blobs" to pop, but these blobs cannot organize; a TC cannot develop. You can't run away from those Westerlies in the Atlantic.
Just look at the WV loop, and this shear map (remember, I pay attention to the orange lines showing the direction, not the speed):
http://cimss.ssec.wisc.edu/tropic/real- ... g8shr.html
http://www.ssd.noaa.gov/goes/east/watl/loop-wv.html
WindRunner:
I have been seeing shear maps used rather excessively this year, and people treating them like they were the bible of tropical cyclone development or something, and you have to remember that these maps can be inaccurate sometimes, by up to 20kts or so. These maps, whether computer or human generated, are subject to inaccuracies just like everything else in the weather world, and need to be taken into consideration with these thoughts in mind. . .
WxGuy1 added more about shear:
More importantly, shear is not an advective property and is often NOT static! Just because a "system" is forecast to move into an area that has little shear NOW does not mean that shear will remain low in that area LATER. In addition, the magnitude of shear does not necessarily 'advect'. Shear is the difference (dir and magn) of flow between two levels. If flow at one level changes, so does the shear. Oftentimes, winds at both levels change, creating situations where shear can change rapidly. This also means that minor errors in wind speed and direction in model forecasts can create major errors in vertical wind shear forecasts. We all know about the dearth of observations (both surface and aloft) in the tropics, so that adds yet another complication / caveat.
Why not examine 500mb and 850mb model output to get an approximation of shear 24+ hrs in advance? Looking at this evening's GFS output, it looks like a 250mb cut-off low move slowly off the southeast US coast, resulting in 20-35kt westerly flow. Any storm that moves westward in this environment will face strong upper-level storm-relative flow, yielding stronger shear (storm-relative shear, since environmental shear is independent of system motion). The 0z NAM output is stronger with this cut-off upper-level low, indicating 40-75kt 250mb northwesterly flow east of Florida in a couple of days. Again, I can't imagine seeing a tropical depression or storm in such an environment. A slightly better bet for an environment favorable for convective organization may present itself if the 0z NAM has it's way in a few days in the Caribbean, south of a cut-off high progged to develop. FWIW, the GFS shows northwesterly upperlevel flow across much of the Caribbean in 48-72hrs, which just goes to show the variability of upper-level forecasts.
And wxman57 again, on shear and development forecasts:
I don't use those shear maps often; again, shear should be a vector, not scalar, quantity. And as WR stated, they aren't really accurate.
I would point out that saying something "has a chance to develop" and saying "it probably will not develop" may mean exactily the same thing. If something has a 5% chance of developing, then there is a chance it could develop, but it probably will not develop (95% chance). The NHC will always say a system has a chance to develop, even when that chance may be tiny. I will always stress the much more likely scenario, but acknowledge when there might be a small chance of development....
The main difference between many of the pro mets here and a number of posters is we can go on living if a system doesn't develop. We don't think it's fun to see how many hurricanes we can get in a season. Hurricanes mean threats to us and to our clients, and many of those people cannot take a hit in their current state of readiness. So we consider the chances that each disturbance will develop very carefully. When a system really has a chance of development it'll become obvious.
It's been mentioned on this thread that many invests are declared each season. That's true. And only a small fraction of them ever amount to anything. That is particularly true early in the season (June/July). So I'll reserve my enthusiasm for development for a system that really has a shot at developing.
thread ended with the area of discussion seemingly no longer of interest:
cycloneye wrote:NRL took out invest 95L.Code: Select all
http://www.nrlmry.navy.mil/tc_pages/tc_home.html
Especially this year, I'd expect pros and amateurs to get impatient with too much optimistic development analysis by amateurs. Wait till we're actually into a track forecast, eh? The informative posts by pros and experts keep it all in perspective.