Tropical Storm Bertha Model Runs

[gatorcane]

Any reason why the western outlier models such as the CMC and UKMET are not in the storm2k graphic on the homepage for the model runs?

To me when I look at this graphic it indicates a sure FISH which we know is not the case yet.

[Recurve]

At the end the GFDL has it a 1004 depression at 59 knots (?). What about the weakish ? low pulling it northward. It looks to head east with nothing seen upstream. Would it (if "it" survives) hang out in this area or get pushed west again with a rebuilding high?



How likely does the GFDL scenario seem?

I can't post the exact link, run generated here: http://tc.met.psu.edu/Model page

[cycloneye]

This is a much weaker run from the EURO and continues to go fishing.

12z EURO

[KWT]

I suspect it would find it hard getting any further north then that, it'd probably get trapped where it is there then maybe slowly head/drift westward until an exit opens up. Thats what I suspect.
I've got a funny feeling this system will get a little further west then the GFDL and GFs progs right now as those models have been well known to have something of a right bias, maybe something a little closer to the UKMO being more likely IMO.

[ekal]

While 1004mb seems high for a tropical storm, note how close the system is to that 1024mb ridge. That would generate a pretty tight pressure gradient -- much tighter than we are accustomed to seeing in the deep tropics with a 1004mb low. Thus the stronger winds.

I think the track is as reasonable as any other model is offering at this point. While it might head west for a few days under that ridge, there would almost certainly be a trof that would turn it out to sea that far north.

[KWT]

ECM weakens this system past 72hrs as it strays too far north, I think its probably a little hasty in that NW movement as its up close to 20N before even 40W on this run by 72hrs then zooms off to the west and decays totally...also interesting it doesn't do anything with the obviously developing EPAC storms either.

[Recurve]

Like to ask for help from those more experienced. I'm trying to learn to read model runs better, want to look at synoptic scale cause I think we're supposed to, not to focus on the closeup of a deepening low, no going "ooh ooh if it gets there it could explode, right?"
I'm not into forecasting competition and you'll never hear me rooting for development when I live on an island. But I do seriously want to understand models better for steering, not how intense it could possibly maybe become if it goes to the right place.
I know it's wrapped up together. But development and intensity guesses are beyond me. Guessed wrong many many times. I'll probably get my butt caught in a rapidly intensifying storm out of the straits someday. So I'm most interested in track and really appreciate any comments on the synoptics.

[Recurve]

I suspect it would find it hard getting any further north then that, it'd probably get trapped where it is there then maybe slowly head/drift westward until an exit opens up. Thats what I suspect.
I've got a funny feeling this system will get a little further west then the GFDL and GFs progs right now as those models have been well known to have something of a right bias, maybe something a little closer to the UKMO being more likely IMO.

Good comment and thanks for explaining.

[Recurve]

While 1004mb seems high for a tropical storm, note how close the system is to that 1024mb ridge. That would generate a pretty tight pressure gradient -- much tighter than we are accustomed to seeing in the deep tropics with a 1004mb low. Thus the stronger winds.

I think the track is as reasonable as any other model is offering at this point. While it might head west for a few days under that ridge, there would almost certainly be a trof that would turn it out to sea that far north.

Thanks for that too. Explains a lot.
Too early in the season not to expect a trof later to again provide an exit?

[MiamiensisWx]

In regards to the model run posted by Recurve, the grid and isobaric analysis depicts the mean sea level pressures at the low levels. In other words, it displays features such as surface ridges, surface troughs, et al. The model indicates a northward turn because of a weakness at the mid and upper levels, which are not displayed on that particular chart. There is a deepening shotwave with intensifying upper level wind vectors (winds) from the southwest, which are resulting in a deepening (intensification) of the baroclinic low over the North Atlantic. At the surface, a trailing cold front is developing (frontogenesis; formation of a front) as the low deepens. The trough at the mid to upper levels is eroding the Azores ridge (at the mid and upper levels), while the cold front at the lower levels is also weakening the ridging at the lower levels. This is resulting in the northward turn depicted by the model. Additionally, the upper low that is currently NE of the Leeward Islands may be another factor for the northward movement as well.

In regards to the intensity, those +50 kt surface winds indicate the system is a TS in the model. It is NOT a depression, contrary to your post. However, as mentioned, the higher ambient pressures and pressure gradient are contributing to the stronger winds, despite an anomalously high central pressure in the lower 1000s. The small size of the TC is another factor that supports those higher winds, as opposed to a larger TC that is also recurving at that latitude.

Did I help, Dave?

Miami

[ekal]

Recurve, synoptic scale is definitely the way to go with model runs that are 4-6 days out. The details may not be correct during that time period, but the synoptics usually are. Every model run I have looked at today forecasts a weakness to develop in the vicinity of 50W, which appears to be caused by the development of a small low between the Azores and the Bermuda highs. You can see it on this frame of the GFS, just to the left of that deep red associated with the Azores high.

http://moe.met.fsu.edu/cgi-bin/gfstc2.cgi?time=2008070212&field=Sea+Level+Pressure&hour=084hr

This weakness starts the system on that WNW-NW track. Later in the period, a mid-latitude trof connects to that weakness and pulls the system in between the ridges.

http://moe.met.fsu.edu/cgi-bin/gfstc2.cgi?time=2008070212&field=Sea+Level+Pressure&hour=144hr

The trof might not be strong enough to yank it through, but in that case, it would likely just drift in that area for a few days before another trof picks it up. I agree that in most circumstances in June and July, a storm at 25N in the middle of the Atlantic has little chance of making it to the coast.

I'll show you something else. For a system that is forecast to be a TS or stronger, it is often better to look at the model output for 500mb, instead of at the surface, since deeper systems tend to be steered at the mid-levels, not the lower-levels. This is the 12z 500mb output from the GFS today.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/carib/gfs/12/index_500_lu_loop.shtml

The numbers are the height of the 500mb atmospheric surface, in meters. Lower heights signify a weakness, towards which tropical cyclones will move. In the loop, lower heights periodically appear in the central Atlantic (breaking the ridge in two), and the model cyclone responds by moving poleward towards the lower heights. I have seen storms where a strong surface ridge is present in the model output, but the storm still moves north right through it (Ernesto comes to mind), because there was a break in the ridge at 500mb.

As you can tell, I am fond of looking at the models, too.

[cycloneye]

NOGAPS almost doesnt see 92L at all.

12z NOGAPS Animation

[Extremeweatherguy]

yeah, the NOGAPS more or less just keeps it as an open wave moving toward the islands.

[Gustywind]

yeah, the NOGAPS more or less just keeps it as an open wave moving toward the islands.

Can you provide me the link please?

[Extremeweatherguy]

yeah, the NOGAPS more or less just keeps it as an open wave moving toward the islands.

Can you provide me the link please?

See cycloneye's post above mine.

[deltadog03]

lol, sounds like models are starting to back off the idea of strong...

[Blown Away]

lol, sounds like models are starting to back off the idea of strong...

It's difficult to see a hurricane in 2-3 days out of this. Models seem to ramp 92L up to fast.

[KWT]

Yep they are backing off a touch on the strong powerful systems they had before and going for something probably a little more realisitic for the time of year.

[deltadog03]

I made mention to this the other day....the models most always do this......

[Aric Dunn]

The Euro.. still keeping on a wnw track then back west towards the end..

12 ECMWF http://www.meteo.psu.edu/~gadomski/ECMW ... floop.html