Tropical Storm Bertha Model Runs

[cycloneye]

18z GFS much weaker and again,going on a fishing expedition.

18z GFS loop

[Recurve]

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

Absolutely great explanation. I should have known that this was SLP chart and surface features, not showing upper lows. I understand about the gradient too, because 1004 didn't seem that low, but the 59 knots would be a TS.

[Recurve]

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 ... loop.shtml

Very good points too, thanks. I do look at the steering winds (http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/winds-dlm.html -- CIMSS) for different layers depending on intensity, but have looked only at SLP model plots.

[cycloneye]

18z GFDL:It does a sharp right rurn around 47w.

357
WHXX04 KWBC 022332
CHGQLM
ATTENTION...NATIONAL HURRICANE CENTER

NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR

TROPICAL DEPRESSION INVEST 92L

INITIAL TIME 18Z JUL 2

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 11.9 20.9 280./ 8.0
6 12.4 21.5 310./ 7.5
12 12.5 22.3 281./ 8.4
18 12.8 23.6 282./12.4
24 13.0 25.0 279./14.6
30 13.1 26.4 273./13.6
36 13.7 27.7 297./13.5
42 14.4 29.2 294./16.3
48 15.3 30.9 297./18.2
54 15.9 32.6 288./18.0
60 16.2 34.3 282./16.4
66 16.5 35.9 281./15.4
72 16.9 37.4 284./15.2
78 17.5 39.2 288./17.8
84 18.0 40.5 293./13.5
90 19.0 42.3 299./19.4
96 19.9 44.1 298./19.4
102 21.1 45.3 313./16.3
108 22.2 46.4 316./14.9
114 23.5 47.0 336./14.3
120 24.6 47.5 333./12.4
126 25.4 47.7 349./ 7.5

[cycloneye]

Moving 275 west at 8 kts.

WHXX01 KWBC 030057
CHGHUR
TROPICAL CYCLONE GUIDANCE MESSAGE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0057 UTC THU JUL 3 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

DISTURBANCE INVEST (AL922008) 20080703 0000 UTC

...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
080703 0000 080703 1200 080704 0000 080704 1200

LAT LON LAT LON LAT LON LAT LON
BAMS 12.1N 21.7W 12.9N 24.4W 13.5N 27.8W 13.8N 31.2W
BAMD 12.1N 21.7W 13.2N 24.0W 14.3N 26.5W 15.7N 29.3W
BAMM 12.1N 21.7W 13.2N 24.3W 14.0N 27.3W 14.8N 30.6W
LBAR 12.1N 21.7W 12.5N 23.8W 13.4N 26.4W 14.3N 29.2W
SHIP 25KTS 30KTS 38KTS 45KTS
DSHP 25KTS 30KTS 38KTS 45KTS

...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
080705 0000 080706 0000 080707 0000 080708 0000

LAT LON LAT LON LAT LON LAT LON
BAMS 13.9N 33.9W 16.3N 37.8W 20.8N 42.6W 24.3N 46.3W
BAMD 17.2N 32.2W 20.0N 38.0W 23.6N 42.9W 28.1N 42.2W
BAMM 15.6N 33.5W 17.6N 39.0W 20.3N 44.2W 23.5N 45.8W
LBAR 15.5N 32.0W 19.0N 37.9W 21.1N 43.3W 24.3N 44.8W
SHIP 52KTS 66KTS 71KTS 71KTS
DSHP 52KTS 66KTS 71KTS 71KTS

...INITIAL CONDITIONS...
LATCUR = 12.1N LONCUR = 21.7W DIRCUR = 275DEG SPDCUR = 8KT
LATM12 = 12.0N LONM12 = 20.4W DIRM12 = 278DEG SPDM12 = 7KT
LATM24 = 11.7N LONM24 = 18.6W
WNDCUR = 25KT RMAXWD = 60NM WNDM12 = 25KT
CENPRS = 1009MB OUTPRS = 1012MB OUTRAD = 120NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM

$$

[Blown Away]

I don't know how much confidence there is in those tracks. Based on the models 92L is predicted to be a TS by tomorrow. Doesn't seem likely at this point.

[cycloneye]

The 00:00 UTC SHIP shear forecast continues to forecast light shear almost thru 120 hours.

Code: Select all

        *   ATLANTIC SHIPS INTENSITY FORECAST       *
                    *     GOES AND/OR OHC INPUT MISSING         *
                    *      INVEST  AL922008  07/03/08  00 UTC   *

TIME (HR)          0     6    12    18    24    36    48    60    72    84    96   108   120
V (KT) NO LAND    25    27    30    33    38    45    52    61    66    69    71    72    71
V (KT) LAND       25    27    30    33    38    45    52    61    66    69    71    72    71
V (KT) LGE mod    25    26    26    28    29    34    39    44    51    57    62    65    66

SHEAR (KTS)        5     2     3     5     6     6     6     4     8     7     9    11    13
SHEAR DIR        134   158   175   175   204   305   310   319   157   204   183   236   221
SST (C)         26.8  26.1  25.5  25.4  25.5  25.1  24.8  25.0  25.3  25.6  25.9  26.3  26.4
POT. INT. (KT)   122   116   111   110   111   108   105   107   109   112   114   116   117
ADJ. POT. INT.   118   115   109   108   110   105   101   103   104   106   106   105   104
200 MB T (C)   -53.8 -53.9 -53.6 -53.0 -53.5 -53.9 -53.6 -54.0 -53.5 -53.8 -53.6 -54.0 -53.7
TH_E DEV (C)       4     4     3     3     4     4     5     5     5     6     7     7     7
700-500 MB RH     82    79    75    75    74    73    62    61    55    49    48    45    46
GFS VTEX (KT)     15    16    18    18    20    20    18    19    18    17    17    18    18
850 MB ENV VOR    61    55    58    78    98   115   133   139   129    96    72    43    11
200 MB DIV        92   105    86    79    75    54    51    41    23    31    61    39    24
LAND (KM)        532   639   754   904  1058  1407  1718  2020  2016  1920  1924  2005  2143
LAT (DEG N)     12.1  12.7  13.2  13.6  14.0  14.8  15.6  16.5  17.6  18.7  20.3  21.8  23.5
LONG(DEG W)     21.7  23.0  24.3  25.8  27.3  30.6  33.5  36.3  39.0  41.8  44.2  45.6  45.8
STM SPEED (KT)    10    14    14    15    16    16    14    14    14    14    12     9     8
HEAT CONTENT       4     1     0     0     0     0     0     0     0     0     0     5     5

  FORECAST TRACK FROM BAMM      INITIAL HEADING/SPEED (DEG/KT):275/  8      CX,CY:  -7/  1
  T-12 MAX WIND:  25            PRESSURE OF STEERING LEVEL (MB):  594  (MEAN=625)
  GOES IR BRIGHTNESS TEMP. STD DEV. 100-300 KM RAD: -99.0 (MEAN=20.0)
  % GOES IR PIXELS WITH T < -20 C    50-200 KM RAD: -99.0 (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.   2.   5.   9.  13.  16.  19.  20.  22.
  VERTICAL SHEAR         1.   3.   5.   6.   9.  11.  14.  15.  15.  15.  15.  14.
  PERSISTENCE            0.  -1.  -1.  -1.  -1.  -1.  -1.  -1.  -1.  -1.   0.   0.
  200/250 MB TEMP.       0.   0.   0.   0.   0.   0.   0.   0.   0.   1.   1.   1.
  THETA_E EXCESS        -1.  -1.  -2.  -3.  -4.  -5.  -7.  -9. -11. -12. -13. -13.
  700-500 MB RH          0.   0.   0.   0.   0.   0.   0.   0.   0.   0.  -1.  -2.
  GFS VORTEX TENDENCY    0.   1.   1.   2.   2.   1.   2.   1.   0.   0.   0.   0.
  850 MB ENV VORTICITY   0.   0.   1.   1.   2.   4.   5.   6.   7.   7.   7.   7.
  200 MB DIVERGENCE      1.   1.   2.   3.   4.   5.   6.   6.   6.   6.   7.   6.
  ZONAL STORM MOTION     0.   0.   0.   0.   1.   1.   1.   1.   1.   1.   1.   1.
  STEERING LEVEL PRES    0.   0.   0.   0.   0.   0.   0.   1.   1.   0.   0.   0.
  DAYS FROM CLIM. PEAK   0.   0.   0.  -1.  -1.  -2.  -2.  -2.  -3.  -3.  -3.  -4.
                        ----------------------------------------------------------
  SUB-TOTAL CHANGE       2.   5.   8.  13.  20.  27.  36.  41.  44.  46.  47.  46.

  SATELLITE ADJUSTMENTS ----------------------------------------------------------
  MEAN ADJUSTMENT        0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.
  GOES IR STD DEV        0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.
  GOES IR PIXEL COUNT    0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.
  OCEAN HEAT CONTENT     0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.
                        ----------------------------------------------------------
  TOTAL ADJUSTMENT       0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.   0.
                        ----------------------------------------------------------
  TOTAL CHANGE (KT)      2.   5.   8.  13.  20.  27.  36.  41.  44.  46.  47.  46.

   ** 2008 ATLANTIC RI INDEX AL922008     INVEST 07/03/08  00 UTC **
           ( 25 KT OR MORE MAX WIND INCREASE IN NEXT 24 HR)
 
 12 HR PERSISTENCE (KT):   0.0 Range:-45.0 to  30.0 Scaled/Wgted Val:  0.6/  1.1
 850-200 MB SHEAR (KT) :   4.4 Range: 35.1 to   3.2 Scaled/Wgted Val:  1.0/  1.5
 D200 (10**7s-1)       :  87.4 Range:-20.0 to 149.0 Scaled/Wgted Val:  0.6/  0.9
 POT = MPI-VMAX (KT)   :  87.1 Range: 25.1 to 130.7 Scaled/Wgted Val:  0.6/  0.7
 850-700 MB REL HUM (%):  76.8 Range: 56.0 to  88.0 Scaled/Wgted Val:  0.6/  0.3
 % area w/pixels <-30 C:9999.0 Range: 17.0 to 100.0 Scaled/Wgted Val:999.0/999.0
 STD DEV OF IR BR TEMP : 999.9 Range: 35.1 to   3.2 Scaled/Wgted Val:999.0/999.0
 Heat content (KJ/cm2) :   1.0 Range:  0.0 to 132.0 Scaled/Wgted Val:  0.0/  0.0
 
 Prob of RI for 25 kt RI threshold=   999% is 999.0 times the sample mean(12.3%)
 Prob of RI for 30 kt RI threshold=   999% is 999.0 times the sample mean( 7.8%)
 Prob of RI for 35 kt RI threshold=   999% is 999.0 times the sample mean( 4.5%)


[Extremeweatherguy]

**The CMC run did not update on this image (as of 8:57am 7/3/08). It is still showing yesterday's run. For an updated run (today's 00z), see my post further down this page**

[MiamiensisWx]

It looks like several of the models have shifted slightly further west, including some of the important globals. I'm suspecting they're latching on to the trends. Regardless, I still expect recurvature, but the approximate location depicted by the models is more plausible now.

[cycloneye]

This 18z GFDL run has 92L briefly reaching hurricane status.

18z GFDL Animation

[Meso]

The 00z EURO has a weak storm in 72 hours and then after about 150 or so hours it opens the low into an open wave and then from there loses the low completely

[KWT]

Yep Meso thats what it did in the 12z run last night as well it must be sensing some shear out there around that time, SHIPS does show shear starting to increase by 120hrs.

General track looks fairly well agreed now though I still think we are going to see some more westward shift in the track the general idea looks pretty well nailed on now.

[cycloneye]

06z GFDL makes a hard right turn at around 46w.

WHXX04 KWBC 031130
CHGQLM
ATTENTION...NATIONAL HURRICANE CENTER

NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR

TROPICAL DEPRESSION TWO 02L

INITIAL TIME 6Z JUL 3

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 12.6 22.3 285./ 7.0
6 12.6 22.9 266./ 5.8
12 13.0 24.1 291./12.4
18 13.3 25.6 282./14.5
24 13.6 26.9 284./13.5
30 14.4 28.2 301./14.9
36 15.2 29.7 298./16.6
42 16.2 31.3 302./17.7
48 16.9 33.0 292./18.0
54 17.8 34.6 299./17.9
60 18.5 36.6 289./19.7
66 19.1 38.6 287./20.0
72 19.5 40.6 280./19.4
78 20.0 42.2 290./15.9
84 20.9 43.8 297./16.8
90 21.7 44.9 306./13.0
96 22.7 45.7 321./13.0
102 23.8 46.2 338./11.8
108 25.0 46.2 356./12.0
114 26.1 46.3 359./10.5
120 27.1 46.2 3./10.5
126 27.9 46.2 3./ 7.9

[KWT]

Very interesting GFDL map it seems to get dragged into the weakness that is pulling helping to drag the system off to the N. Its going to have to speed up if its going to take that route though, still think a more typical NW track like the NHC show is the best option.

[chadtm80]

[Extremeweatherguy]

The 00z CMC run is interesting...

http://moe.met.fsu.edu/cgi-bin/cmctc2.c ... =Animation

[Meso]

CMC at the end shows the ridge breaking down rather fast which should move it North before it has any chance of landfall,and there appears that the ridge wont fill in soon enough to make any more of a westerly movement, though stranger things have happened

[cycloneye]

There was an error in the release of the 12:00 models as they repeated the 6:00 UTC ones.

[gatorcane]

Note the CMC actually pushes this thing due West for quite some time before it makes a WNW to NW turn...a little too close for comfort for the Caribbean islands (NE Leewards)

[Extremeweatherguy]

Note the CMC actually pushes this thing due West for quite some time before it makes a WNW to NW turn...a little too close for comfort for the Caribbean islands (NE Leewards)

Exactly my thoughts. If the ridge doesn't break down like the CMC is showing at the very end of the run, then this storm could wind up getting dangerously close to the islands. Hopefully the CMC is wrong with its due W/WNW motion for the next few days.