Tropical Storm Bertha Model Runs

[cycloneye]

I am hoping it will stay a weak TS and hit NC as a depression or storm because we REALLY need the rain.

I understand that the area is having fires around the state.

[Aric Dunn]

What I see is the right most models now coming in line with the other model guidence, kindeed the models are in good agreement on a WNW track out to 50W. UKMO and nogaps which don't do much with this system still obn the southern side of the guidence.

If I was in Bermuda I'd be keeping a close eye just in case on this system given there is less of a chance of a major recurve now.

Also strong system on the GFDL as well as has been mentioned.

thats correct.. but wait for the hwrf to update on that image.. its way left almost NE carribean and the euro is not on there but when the 12z comes out i bet its going to be inline with hwrf

[Aric Dunn]

1

[Aric Dunn]

ok here is the update....

so what are they doing now? trending westward... .. of course its because they are all forecasting a weaker storm initially. but thats the point

how far west do you think the nhc is going to shift .. they are not going to stay where they are.. lol .. that my dear friend is a trend..

[txwatcher91]

I am hoping it will stay a weak TS and hit NC as a depression or storm because we REALLY need the rain.

I understand that the area is having fires around the state.

Yes, there have been several large fires around the area. One of them had most of the state covered in smoke for about a week before the winds shifted and blew the smoke back out to sea. The grass in this area sounds like potato chips when you walk on it, and there are many trees losing their leaves already. It truly is getting bad, already worse than last year. I am really hoping for a weak TS to come and give us some much needed rain.

[KWT]

hmm models are shifting westward, maybe the models are seeing a slightly slower foward speed ( I do remember when GFDL took the hard right path it progged it to reach 18-20kts by Sat-Sun) and therefore the weakness isn't quite as strong allowing the system to carry on going to the WNW.

As for the NHC, well the models are now bang in line with the offical track so I think they will keep it about where it is now but may note the westward shift in the discussion.

[jhamps10]

ok here is the update....

so what are they doing now? trending westward... .. of course its because they are all forecasting a weaker storm initially. but thats the point

how far west do you think the nhc is going to shift .. they are not going to stay where they are.. lol .. that my dear friend is a trend..

That most certainly is a trend. I'd say that it will go west and end up in the middle of the guidence, Bremuda I'd keep a close eye on this one.

[cycloneye]

The latest SHIP shear forecast calls for light shear until 108 hours.

Code: Select all

           *   ATLANTIC SHIPS INTENSITY FORECAST       *
                    *        GOES/OHC INPUT INCLUDED            *
                    *      BERTHA  AL022008  07/03/08  18 UTC   *

TIME (HR)          0     6    12    18    24    36    48    60    72    84    96   108   120
V (KT) NO LAND    35    39    43    47    50    57    61    65    68    70    66    65    59
V (KT) LAND       35    39    43    47    50    57    61    65    68    70    66    65    59
V (KT) LGE mod    35    37    40    42    44    49    54    59    65    70    73    71    65

SHEAR (KTS)        5     3     8     9     5     5     7     3     3    15    15    30    35
SHEAR DIR        138   260   253   245   218   207   107   188   179   240   222   231   248
SST (C)         25.4  25.4  25.5  25.4  25.1  24.7  25.1  25.5  25.8  26.4  26.8  26.9  26.9
POT. INT. (KT)   109   109   111   110   108   105   108   111   114   120   123   123   122
ADJ. POT. INT.   105   106   108   107   105   102   105   108   110   114   115   111   108
200 MB T (C)   -53.1 -53.7 -54.1 -53.9 -53.3 -54.2 -53.5 -53.8 -53.4 -53.6 -53.5 -53.3 -53.5
TH_E DEV (C)       4     4     4     4     4     4     5     6     6     7     8     8     8
700-500 MB RH     76    75    76    72    72    69    59    57    52    50    46    44    46
GFS VTEX (KT)     17    17    18    19    19    21    19    19    18    20    16    20    18
850 MB ENV VOR    52    70    70    74    84   108   106    92    68    63    46    28    17
200 MB DIV        56    65    54    24    52    64    26    19    40    55    35    22    -2
LAND (KM)        823   948  1077  1230  1385  1741  2099  1962  1828  1824  1780  1667  1633
LAT (DEG N)     13.4  13.8  14.2  14.7  15.1  16.1  17.1  18.0  19.0  20.5  22.5  24.2  25.7
LONG(DEG W)     25.0  26.3  27.5  29.0  30.4  33.7  37.0  40.3  43.7  46.7  49.2  50.9  52.0
STM SPEED (KT)    12    13    14    15    16    17    17    16    16    16    14    10     8
HEAT CONTENT       0     0     0     0     0     0     0     0     0     6    13    13    12

  FORECAST TRACK FROM OFCI      INITIAL HEADING/SPEED (DEG/KT):285/ 10      CX,CY:  -9/  3
  T-12 MAX WIND:  30            PRESSURE OF STEERING LEVEL (MB):  545  (MEAN=625)
  GOES IR BRIGHTNESS TEMP. STD DEV. 100-300 KM RAD:  15.4 (MEAN=20.0)
  % GOES IR PIXELS WITH T < -20 C    50-200 KM RAD:  87.0 (MEAN=68.6)

                        INDIVIDUAL CONTRIBUTIONS TO INTENSITY CHANGE
                         6   12   18   24   36   48   60   72   84   96  108  120
                        ----------------------------------------------------------
  SAMPLE MEAN CHANGE     1.   2.   3.   4.   6.   8.   9.  10.  11.  12.  12.  13.
  SST POTENTIAL          0.   0.   0.   0.   0.   2.   5.   8.  10.  12.  13.  14.
  VERTICAL SHEAR         1.   2.   3.   5.   7.   9.  12.  13.  13.  12.   9.   5.
  PERSISTENCE            1.   1.   2.   2.   3.   2.   2.   2.   2.   1.   1.   0.
  200/250 MB TEMP.       0.   0.   0.   0.   0.   0.   0.   0.   0.   1.   1.   1.
  THETA_E EXCESS         0.  -1.  -2.  -2.  -3.  -5.  -6.  -8. -10. -11. -11. -12.
  700-500 MB RH          0.   0.   0.   0.   0.   0.   0.   0.   0.   0.  -1.  -1.
  GFS VORTEX TENDENCY    0.   0.   1.   1.   2.   1.   0.   0.   1.  -2.   1.  -1.
  850 MB ENV VORTICITY   0.   1.   1.   1.   2.   3.   4.   5.   5.   5.   5.   5.
  200 MB DIVERGENCE      0.   1.   1.   1.   2.   3.   3.   3.   3.   4.   3.   3.
  ZONAL STORM MOTION     0.   0.   0.   1.   1.   1.   1.   2.   2.   2.   2.   2.
  STEERING LEVEL PRES    0.   0.   0.   1.   1.   1.   1.   2.   2.   2.   1.   1.
  DAYS FROM CLIM. PEAK   0.   0.   0.  -1.  -1.  -2.  -2.  -2.  -3.  -3.  -3.  -4.
                        ----------------------------------------------------------
  SUB-TOTAL CHANGE       3.   6.   9.  13.  20.  24.  30.  35.  38.  34.  33.  26.

  SATELLITE ADJUSTMENTS ----------------------------------------------------------
  MEAN ADJUSTMENT        0.   0.   0.   0.  -1.  -1.  -1.  -1.  -1.  -1.  -1.  -2.
  GOES IR STD DEV        1.   1.   2.   2.   2.   2.   1.   0.  -1.   0.   0.   0.
  GOES IR PIXEL COUNT    0.   0.   1.   1.   1.   0.   0.   0.   0.   0.   0.   0.
  OCEAN HEAT CONTENT     0.   0.   0.   0.   0.   0.  -1.  -1.  -1.  -1.  -1.  -1.
                        ----------------------------------------------------------
  TOTAL ADJUSTMENT       1.   2.   2.   2.   2.   1.   0.  -2.  -3.  -3.  -3.  -3.
                        ----------------------------------------------------------
  TOTAL CHANGE (KT)      4.   8.  12.  15.  22.  26.  30.  33.  35.  31.  30.  24.

   ** 2008 ATLANTIC RI INDEX AL022008     BERTHA 07/03/08  18 UTC **
           ( 25 KT OR MORE MAX WIND INCREASE IN NEXT 24 HR)
 
 12 HR PERSISTENCE (KT):   5.0 Range:-45.0 to  30.0 Scaled/Wgted Val:  0.7/  1.2
 850-200 MB SHEAR (KT) :   6.2 Range: 35.1 to   3.2 Scaled/Wgted Val:  0.9/  1.4
 D200 (10**7s-1)       :  50.2 Range:-20.0 to 149.0 Scaled/Wgted Val:  0.4/  0.6
 POT = MPI-VMAX (KT)   :  71.4 Range: 25.1 to 130.7 Scaled/Wgted Val:  0.4/  0.5
 850-700 MB REL HUM (%):  76.0 Range: 56.0 to  88.0 Scaled/Wgted Val:  0.6/  0.3
 % area w/pixels <-30 C:  78.0 Range: 17.0 to 100.0 Scaled/Wgted Val:  0.7/  0.2
 STD DEV OF IR BR TEMP :  10.3 Range: 35.1 to   3.2 Scaled/Wgted Val:  0.8/  1.0
 Heat content (KJ/cm2) :   0.0 Range:  0.0 to 132.0 Scaled/Wgted Val:  0.0/  0.0
 
 Prob of RI for 25 kt RI threshold=    38% is   3.1 times the sample mean(12.3%)
 Prob of RI for 30 kt RI threshold=     3% is   0.3 times the sample mean( 7.8%)
 Prob of RI for 35 kt RI threshold=     1% is   0.3 times the

[ronjon]

12Z Euro takes a weaker system to about 22N-60W in 6-7 days and then stalls and weakens it.

http://www.ecmwf.int/products/forecasts/d/animate/catalog/products/forecasts/medium/deterministic/msl_uv850_z500!Wind%20850%20and%20mslp!240!North%20America!pop!od!oper!public_plots!2008070312!!step/

[Aric Dunn]

hmm models are shifting westward, maybe the models are seeing a slightly slower foward speed ( I do remember when GFDL took the hard right path it progged it to reach 18-20kts by Sat-Sun) and therefore the weakness isn't quite as strong allowing the system to carry on going to the WNW.

As for the NHC, well the models are now bang in line with the offical track so I think they will keep it about where it is now but may note the westward shift in the discussion.

ummmm.. not quite..

here is the the NHC thinking ...

"THE NEW OFFICIAL FORECAST IS A LITTLE
FASTER AND NORTH OF THE PREVIOUS TRACK AND IS CLOSE TO A CONSENSUS
OF THE GFDL...GFS...HWRF...AND ECMWF MODELS. "

so lets start the gfs and gfdl are in fairly good agreement with the nhc now.. but the ecmwf has not come in yet but the HWRF is way way west from is previous run and to note also that the ECMWF has been the left most model the whole time so i imagine it will not change much during this run so now there is a problem the 4 models that the nhc said had a consensus!! are now no longer in agreement .. so the nhc will have to adjust there forecast west and I imagine it will been right down the middle of the 4 models so a average.

[Aric Dunn]

12Z Euro takes a weaker system to about 22N-60W in 6-7 days and then stalls and weakens it.

http://www.ecmwf.int/products/forecasts/d/animate/catalog/products/forecasts/medium/deterministic/msl_uv850_z500!Wind%20850%20and%20mslp!240!North%20America!pop!od!oper!public_plots!2008070312!!step/

so ok yeah the 12z has not changed much if anything its even more west .. so the 4 models are now the extremes.. so what to do .. hhhmmmm... lets split the difference..

[Aric Dunn]

nogaps about the same keeps it weaker and west ...

http://moe.met.fsu.edu/cgi-bin/ngptc2.c ... =Animation

[KWT]

Yep Aric but the GFS and GFDL have now come inline with the NHC thinking, if those models were now to the left of the NHC track then they may shift it but its not so theres no real reason why they should move it.

I suspect the ECM weakens this for the same reason as the SHIPS, an increase of shear, 35kts of shear from the ships which a hefty blow.

[Derek Ortt]

more like wave in 24-36 hours

afternoon model runs are somewhat encouraging, but we need to wait for the 0Z to make any definite trends

[Aric Dunn]

more like wave in 24-36 hours

afternoon model runs are somewhat encouraging, but we need to wait for the 0Z to make any definite trends

there is that encouraging thing again.... weaker now does not mean weak the whole time .. weaker now only means more westerly and potentially stronger later and heading towards some land somewhere..

[KWT]

The thing is the mode;ls that do weaken this back into an open wave do have lower resolution then say the GFS and other models based off its data and whilst it may not mean anything it could at least help to explain why they weaken this as much as they do.

Equally they could be just responding to the much lower heat content in the way of this system and the GFS does have a habit of overdoing convective feedback sometimes.

[Aric Dunn]

well here is the hwrf loop the better one..

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

[Derek Ortt]

except the models are NOT redeveloping this farther west, Aric

as I said, we need to wait for one more run before drawing conclusions. But this is definately encouraging compared to 36 hours ago

[Aric Dunn]

except the models are NOT redeveloping this farther west, Aric

as I said, we need to wait for one more run before drawing conclusions. But this is definately encouraging compared to 36 hours ago

actually lol thats the point Derek.. models dont do every well with intensity..... and the hwrf does re-strengthen at the end.......................................................... weaker now keeps it more west over slight warmer ssts which would allow for potential strengthening.. of course yes its possible either way but going north and out to see leave very little chance of intensification if the ssts are cooler..and more stable air

[KWT]

True Derek I suspect the reason is once the models opens up the low it then reaches the shear and that prevents any further re-development, thats my best guess though based on what I've seen.