Tropical Storm Bertha Model Runs

[Nimbus]

With computer models its garbage in / garbage out if the data changes too fast.
It can take several model runs before new data migrates the forecast.

There are a couple new observations that were not in the prior data sets.
1. Bertha is now a much stronger Hurricane than initialized in prior runs.
Although short term increased strength should cause her to slow down and turn poleward it may have other consequences.

If Berthas strength pumps up the ridge she is now moving into it could change the timing of the first trough encounter.
A stronger ridge might turn her back a little toward the west as the BAM models are signaling for example.

2. Her slower forward speed means she may not gain latitude quickly enough for the first trough to take her out to sea.
The two high pressure areas might even bridge and that would at the very least cause a major delay in recurving the system.

As others have mentioned this is not an easy "Bermuda or not" forecast.

[KWT]

I think we will end up seeing the models re-adjusting back to the west again soon enough, remember the l;ast weakness was over-done by the models at this range and I think this one may be as well...offical track tohugh is probably close to the mark.

SHIPS do forecast shear to increase quite a bit but then they have been very poor so far with the shear forecasts so I'm not going to read too much into that.

[RL3AO]

I think we will end up seeing the models re-adjusting back to the west again soon enough, remember the l;ast weakness was over-done by the models at this range and I think this one may be as well...offical track tohugh is probably close to the mark.

SHIPS do forecast shear to increase quite a bit but then they have been very poor so far with the shear forecasts so I'm not going to read too much into that.

I agree. I don't see this going east of Bermuda.

[KWT]

Besides the GFDL has this at about 310 right now and so unless it does pick up some latitude thats likely going to be a little too far east and if this is a hurricane then even if the system does go a little to the east the island of Bermuda will still possible come under hurricane watches/warnings.

[Steve]

http://euler.atmos.colostate.edu/~vigh/ ... early1.png

18z early track guidance

[DESTRUCTION5]

http://euler.atmos.colostate.edu/~vigh/guidance/northatlantic/track_early1.png

18z early track guidance

Here we go with the split camp again!

[PTrackerLA]

AEMN is the GFS correct? Quite a difference in opinion between that and the BAM models as compared to the rest of the globals.

[Steve]

>>AEMN is the GFS correct? Quite a difference in opinion between that and the BAM models as compared to the rest of the globals.

Most of those plots are GFS Operational derived (not NOGAPS, Xtrap or Official for sure and maybe 1 or two others).

Steve

[LAwxrgal]

Well right now it's only the BAMMs that are going with the idea of Bertha crawling underneath a ridge. Here's the thing about that though, the BAMMs, from what I understand, are for shallow storms, and I don't think Bertha qualifies. We just have to see if the BAMMs are just outliers or are they really on to something. The rest of the models recurve this.

It's pretty much a known fact that Bertha will recurve, the question is when?

[Steve]

>>Well right now it's only the BAMMs that are going with the idea of Bertha crawling underneath a ridge. Here's the thing about that though, the BAMMs, from what I understand, are for shallow storms, and I don't think Bertha qualifies.

"M" is the medium, "S" is shallow, and "D" is deep. They are tropical models which according to those who know don't perform as well out of the tropics.

Steve

[KWT]

for this system the BAMD is the best one to use but they will not be able to handle the evolution of this pattern and so should only be used for maybe the track in the next 12-24hrs at most as they are only statistical models.

[Ivanhater]

Looking like she will turn and most likely not affect the CONUS, but at least something to track in early July when there is usually nothing...gave a chance for us all to dust off our model and tracking skills for the upcoming season...

[x-y-no]

The BAM models run off the operational GFS grid with no dynamic feedback. Note that BAMD is closest to the dynamic models, so that's an indication of the current deep steering.

And the GFS has Bertha way too weak which biases the steering later in the period, which is why all the BAM models have that turn left at the end.

[PTrackerLA]

Got it thanks for the explanations I get a rusty when it comes to all these models during the off season. No doubt in my mind this one's staying out in the Atlantic and let's hope Bermunda is spared. I wonder if we'll see another big storm this July or if this was just an early season fluke? Time will tell.

[Extremeweatherguy]

Got it thanks for the explanations I get a rusty when it comes to all these models during the off season. No doubt in my mind this one's staying out in the Atlantic and let's hope Bermunda is spared. I wonder if we'll see another big storm this July or if this was just an early season fluke? Time will tell.

yeah, I agree. Is this just a one and done situation or will we see something more like July 2005, July 2003 or July 1997 where we had multiple tropical storms and hurricanes? I guess we will just have to wait and see...

July 2005
5 Total Storms
2 Tropical Storms
3 Hurricanes (2 Major)

July 2003
5 Total Storms
2 Tropical Depressions
1 Tropical Storm
2 Hurricanes (0 Major)

July 1997
5 Total Storms
1 Tropical depression
2 Tropical Storms
2 Hurricanes (0 Major)

[Derek Ortt]

of note about July 1997:

Named storms that formed from tropical waves: 0

In 2003 we had 2 and in 2005 we had 6

[wxman57]

of note about July 1997:

Named storms that formed from tropical waves: 0

In 2003 we had 2 and in 2005 we had 6

I think that depends on how you define "formed from tropical waves" as far as 2005. I just went back and counted about 18 that formed from waves in 2005. They didn't form east of the Caribbean, but they formed as the waves reached either the NW Caribbean, the Gulf, or the BoC and interacted with upper lows or upper trofs. But we did track them all the way from Africa, whether or not they had any significant convection.

[Derek Ortt]

I meant before August we had 6 storms from waves

thinking back... we had 7 as Franklin was also from a wave. bad Derek

[Emmett_Brown]

Sorry, i am a forgetful old man... can someone remind me when the next model runs come in?

[cycloneye]

18z GFDL crawls Bertha and tracks east of Bermuda.

WHXX04 KWBC 072332
CHGQLM
ATTENTION...NATIONAL HURRICANE CENTER

NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR

HURRICANE BERTHA 02L

INITIAL TIME 18Z JUL 7

DISCLAIMER ... THIS INFORMATION IS PROVIDED AS GUIDANCE. IT
REQUIRES INTERPRETATION BY HURRICANE SPECIALISTS AND SHOULD
NOT BE CONSIDERED AS A FINAL PRODUCT. PLEASE SEE THE TPC/NHC
OFFICIAL FORECAST.


FORECAST STORM POSITION

HOUR LATITUDE LONGITUDE HEADING/SPEED(KT)

0 19.9 51.6 290./12.0
6 20.6 52.3 317./ 9.1
12 21.2 53.1 307./10.5
18 21.9 54.0 307./ 9.9
24 22.5 54.8 308./10.3
30 23.0 55.6 303./ 8.5
36 23.5 56.5 299./ 9.5
42 24.1 57.2 307./ 9.4
48 24.8 58.0 312./ 9.6
54 25.4 58.5 320./ 7.6
60 26.1 59.2 318./ 9.7
66 27.0 59.7 331./ 9.2
72 27.8 60.0 334./ 8.6
78 28.4 60.3 335./ 7.3
84 29.1 60.7 331./ 7.6
90 29.6 61.0 329./ 5.8
96 30.1 61.2 340./ 5.0
102 30.6 61.3 352./ 4.7
108 31.0 61.4 337./ 3.8
114 31.2 61.3 32./ 3.1
120 31.7 61.2 9./ 4.6
126 32.0 60.9 43./ 4.6