Tropical Storm Bertha Model Runs

[Fego]

GFS put Bertha in the central Atlantic, but shows a less organized systems toward the Caribbean. Time to look for consistency .

[Meso]

00z Ukmet weakens it and moves it West, just North East of Puerto Rico, but weak.

[Jam151]

The new ECMWF run shows it almost running into Cape Hatteras by day 10. It maintains Bertha as a TC through the period this time too.

[jinftl]

Be curious to learn if there is anything to this observation from the pros...it almost seems that for the last few seasons (maybe from 2004 on), there has been a bias for the models to turn storms out to sea initially, only to shift west, and closer to the U.S. (or Caribbean islands) over time.

any accuracy to that observation?

[Meso]

I'm not a pro but I'll give you my thoughts on the situation.

I think the main reason for the trends to the West in terms of model runs in the Eastern Atlantic is due to the fact that models usually intensify the storm too quickly or too strong, thus giving it a more Northerly movement originally.But as time goes by and the storm strengthens at a slower pace the models are then initialized with that data and thus have a better handle of the system, hence showing a weaker storm which will track more West.


This isn't always the case as models often shift to the right as well, but I have too noticed that trend over the years.

Just my thoughts on the situation,I may be wrong

[Derek Ortt]

its due to a lack of data over the ocean

a model is prone to large error if the initial conditions are not correct. Having a limited amount of data over the ocean results in the initial conditions being prone to large error

[jinftl]

Some westward shift in forecast continues with new 5am advisory


TROPICAL STORM BERTHA DISCUSSION NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008
500 AM EDT FRI JUL 04 2008

THE FORECAST REASONING HAS NOT CHANGED TOO MUCH. THE FIRST TWO DAYS
OF THE TRACK FORECAST HAVE BEEN ADJUSTED SLIGHTLY NORTHWARD...
MAINLY TO ACCOUNT FOR THE CHANGE IN THE INITIAL MOTION.
THEREAFTER...ONCE BERTHA FINDS ITSELF DUE SOUTH OF THE MID-LEVEL
RIDGE TO ITS NORTH...THE TRACK HAS BEEN SPED UP AND EDGED A LITTLE
TO THE LEFT OR WEST...IN ACCORDANCE WITH A WESTWARD SHIFT IN MOST
OF THE MODELS. ALL OF THE MODELS STILL FORECAST A WEAKNESS IN THE
RIDGE TO ALLOW BERTHA TO TURN TO THE RIGHT LATE IN THE FORECAST
PERIOD...BUT RECENT RUNS HAVE BEEN TRENDING TOWARD DELAYING THIS
TURN. THE NEW OFFICIAL TRACK FORECAST IS KEPT CLOSE TO THE MODEL
CONSENSUS...BUT THE MODEL SPREAD IS SUBSTANTIAL AT DAYS 4-5. THE
MODELS THAT FORECAST A STRONGER BERTHA...SUCH AS THE
GFDL...FORECAST MORE OF A NORTHWESTWARD MOTION BY DAY 5...WHILE
MODELS SUCH AS THE ECMWF AND UKMET INSIST ON A WEAKER CYCLONE
CONTINUING WEST-NORTHWESTWARD. THE OFFICIAL INTENSITY
FORECAST...LIKE THE TRACK FORECAST...IS CLOSE TO THE
CONSENSUS...TAKING A STRONG TROPICAL STORM DOWN THE MIDDLE OF THE
GUIDANCE ENVELOPE...IN CLOSEST AGREEMENT WITH THE LGEM GUIDANCE.
STRENGTHENING SHOULD BE LIMITED BY COOL WATERS DURING THE NEXT TWO
DAYS...AND BY INCREASING SHEAR ON DAYS 4 AND 5. IT IS NOTABLE THAT
THE GFDL AND HWRF INTENSITY FORECASTS ARE VERY MUCH IN
DISAGREEMENT...INDICATIVE OF GREAT UNCERTAINTY IN THE INTENSITY
FORECAST AS WELL.

[KWT]

Also I note with the models that they can sometimes under-estimate heights of high pressure cells, indeed even here in the Uk I've noticed that sometimes the GFS noteably will big time overdo low pressure cells outside of 120hrs and I can only guess that is also the case for upper features as well.

GFS still shifting westwards in its track, now turning NW close to 60W which is very key because that really does bring Bermuda into the frame...

I think another major factor has to be that the GGFS/GFDL did have the system moving at 18-20kts for much of the run, thats probably why it went hard right a few days ago because the weakness is stronger sooner and the longer it takes to get there the less effect the weakness is going to have, esp if it doesn't get any stronger.

[KWT]

06z GFS coming out and has a much weaker storm this run:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_078l.gif

Also a good deal further south closer to the ECm/UKMO as well...
Also makes another Cape Verde storm by 108hrs.

[ronjon]

A review of this mornings models has shown a dramatic shift to the south and west over the long term. The 00Z Euro now brings the storm, albeit a weaker version, toward the Bahamas and N. Carolina coast (still a couple hundred miles offshore though) in the long range. The 06Z GFS has shifted toward yesterdays 12Z Euro track and now brings the system just N of the Leeward Islands. The 00Z UKMET brings the system into the N Leeward Islands. While things can change, Bertha now looks like it has the potential to impact the N. Leewards, Bermuda, the Bahamas, and the east coast of the US. All models except the CMC weaken the system with time. Stay tuned - we have a long time to watch this one. I hate to say it, but JB could end up being right on this one.

[Blown Away]

What was JB's conclusion on Bertha?

[cycloneye]

This is the most west GFDL has been in the track of Bertha from all the past runs.

WHXX04 KWBC 041130
CHGQLM
ATTENTION...NATIONAL HURRICANE CENTER

NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR

TROPICAL STORM BERTHA 02L

INITIAL TIME 6Z JUL 4

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 13.7 27.6 285./12.0
6 14.6 28.6 313./12.9
12 15.4 30.4 296./19.0
18 16.1 32.2 291./18.5
24 16.7 34.2 284./20.5
30 17.0 36.1 281./18.6
36 17.4 38.4 279./21.9
42 17.6 40.3 277./18.7
48 18.0 42.4 281./19.6
54 18.5 44.4 284./19.9
60 19.2 46.2 290./18.3
66 20.0 47.8 295./16.9
72 20.3 49.3 284./14.9
78 20.9 50.5 296./11.6
84 21.6 51.4 307./11.3
90 22.2 52.4 302./11.4
96 22.9 53.4 303./11.0
102 23.5 54.3 306./11.0
108 24.3 55.2 311./10.5
114 25.0 55.9 317./10.2
120 25.7 56.9 304./11.2
126 26.3 57.7 304./ 8.8

[ronjon]

:uarrow: What was JB's conclusion on Bertha?

A couple of days ago he said it would be a threat to the SE US.

[cycloneye]

What!! A cat 3 from GFDL,101 kts? Are you kidding me? I am not snarking,look at the animation.

http://moe.met.fsu.edu/cgi-bin/gfdltc2. ... =Animation

[cycloneye]

HWRF is a different story from GFDL as it mantains a strong Tropical Storm thru all the run.

http://moe.met.fsu.edu/cgi-bin/hwrftc2. ... =Animation

[Blown Away]

The problem I have w/ the GFDL is speed, it has Bertha going from her current speed of 14mph to nearly 24mph in 24 hours. Just hard to grasp that rapid increase in speed over 24 hours.

[crownweather]

Can someone post a link to the text output of the HWRF model??

Thanks!!

[cycloneye]

Now up to 45kts,1000 mbs

WHXX01 KWBC 041239
CHGHUR
TROPICAL CYCLONE GUIDANCE MESSAGE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1239 UTC FRI JUL 4 2008

DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.
PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE
AND SUBTROPICAL CYCLONE INFORMATION.

ATLANTIC OBJECTIVE AIDS FOR

TROPICAL CYCLONE BERTHA (AL022008) 20080704 1200 UTC

...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
080704 1200 080705 0000 080705 1200 080706 0000

LAT LON LAT LON LAT LON LAT LON
BAMS 14.7N 29.0W 16.2N 32.3W 17.8N 36.1W 18.7N 40.0W
BAMD 14.7N 29.0W 15.9N 31.8W 17.1N 34.8W 18.2N 38.0W
BAMM 14.7N 29.0W 16.2N 31.9W 17.5N 35.2W 18.7N 38.7W
LBAR 14.7N 29.0W 15.9N 31.8W 17.4N 35.1W 19.0N 38.3W
SHIP 45KTS 49KTS 54KTS 56KTS
DSHP 45KTS 49KTS 54KTS 56KTS

...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
080706 1200 080707 1200 080708 1200 080709 1200

LAT LON LAT LON LAT LON LAT LON
BAMS 19.2N 44.6W 19.9N 52.5W 20.0N 58.8W 21.1N 63.0W
BAMD 19.3N 41.0W 21.8N 45.9W 23.7N 48.2W 24.0N 48.2W
BAMM 19.6N 42.2W 21.7N 48.0W 23.5N 51.9W 25.2N 54.9W
LBAR 20.2N 41.3W 22.7N 45.4W 24.6N 45.2W 24.4N 42.2W
SHIP 59KTS 65KTS 64KTS 57KTS
DSHP 59KTS 65KTS 64KTS 57KTS

...INITIAL CONDITIONS...
LATCUR = 14.7N LONCUR = 29.0W DIRCUR = 290DEG SPDCUR = 14KT
LATM12 = 13.5N LONM12 = 26.4W DIRM12 = 289DEG SPDM12 = 12KT
LATM24 = 13.1N LONM24 = 24.0W
WNDCUR = 45KT RMAXWD = 30NM WNDM12 = 40KT
CENPRS = 1000MB OUTPRS = 1012MB OUTRAD = 180NM SDEPTH = D
RD34NE = 75NM RD34SE = 30NM RD34SW = 0NM RD34NW = 75NM

[Extremeweatherguy]

:uarrow: What was JB's conclusion on Bertha?

A couple of days ago he said it would be a threat to the SE US.

Latest from JB this morning = He thinks the storm will get to at least 70W before crossing 25N, meaning it could potentially be a threat to the east coast of the U.S. or the Canadian Maritimes.

[KWT]

Interesting cycloneye you can relaly see the difference between the different sterring levels, a weak storm is more likely to get further west, only at 21N near the longitutde of Bermuda yet the BAMD is only at 48W and at 24N!
Big difference!

As for the GFDL, I do notice its still going for a strong hurricane though IMO the HWRF is more likely in terms of strength though IMO track may be a little too quick to the north.