Frances Advisories

[LowMug]

floyd went from 135KT to 105KT is 6-12 hours during its replacement. These replacements really do take a lot out. These changes usually are not represented in the advisories, but only in Best Track (so dont expect to see the fluctuations represented in real time, only after the season is over

Thanks for that...I was not aware of Floyd's drop off in intensity...I wonder if that was a special case or common

[Air Force Met]

floyd went from 135KT to 105KT is 6-12 hours during its replacement. These replacements really do take a lot out. These changes usually are not represented in the advisories, but only in Best Track (so dont expect to see the fluctuations represented in real time, only after the season is over

Another thing that is not represented is the way the wind works down to the surface more efficiently in a rapidly deepening storm...than one that is weakening.

Let's say you have 2 storms...both with flight level winds of 120 kts. Storm one is weakening during an ERC...then the max sfc winds may really only be 85 or 90 kts. Storm B is explosively deepening. That storm may have sfc winds of 105-110 kts. That is why Charley was so dangerous...and Andrew. They were on the deepening side of their cycles and more of the strong winds aloft worked down to the sfc.

[PurdueWx80]

floyd went from 135KT to 105KT is 6-12 hours during its replacement. These replacements really do take a lot out. These changes usually are not represented in the advisories, but only in Best Track (so dont expect to see the fluctuations represented in real time, only after the season is over

Another thing that is not represented is the way the wind works down to the surface more efficiently in a rapidly deepening storm...than one that is weakening.

Let's say you have 2 storms...both with flight level winds of 120 kts. Storm one is weakening during an ERC...then the max sfc winds may really only be 85 or 90 kts. Storm B is explosively deepening. That storm may have sfc winds of 105-110 kts. That is why Charley was so dangerous...and Andrew. They were on the deepening side of their cycles and more of the strong winds aloft worked down to the sfc.

Same story with Alex...and Claudette last year.

[bigmike]

so derek are you saying you think the track forecast from nhc will change? I'm assuming you think that francis will trend more northward than westward? Sorry newbie here

[Dean4Storms]

floyd went from 135KT to 105KT is 6-12 hours during its replacement. These replacements really do take a lot out. These changes usually are not represented in the advisories, but only in Best Track (so dont expect to see the fluctuations represented in real time, only after the season is over

That was not all that was going on when Floyd weakened. He entrained drier air and if memory serves he encountered some vertical shear. Not saying that the eyewall replacement didn't have it's effects but it was NOT the sole reason why Floyd weakened from 135kt. to 105kt.

[flyingphish]

Thanks for the stat's Dixie ! Been a busy year !!!

[Derek Ortt]

The shear from Floyd was after the eye wall cycle was completed. The shear is the reason why the winds only recovered to 120KT, instead of coming all the way back

[Dean4Storms]

I wanted to point this out with some factual info. so nobody thinks I'm jawing Derek. I'm not, I respect his opinions and recognize professionalism.

From NHC archives on Floyd's weakening.......


Although there was a fluctuation in intensity, related to an eyewall replacement event discussed in the next section, overall the intensity of Floyd diminished from the 13th to the 15th. Environmental causes for intensity change are not entirely understood, but two large-scale factors probably contributed to a gradual decline: the entrainment of drier air at low levels from the northwest, and increasing south-southwesterly vertical shear. As Floyd neared the North Carolina coast late on the 15th, its maximum winds decreased below category three status.

[Derek Ortt]

we had a numerical simulation at rsmas that showed the weakeing, but then it didnt continue to weaken as we didnt get the shear. No doubt the shear got Floyd at the end, sparing the coast from a 4 (and probably the upwelled waters from Dennis)

[Brent]

Hurricane Frances Advisory Number 13

Statement as of 11:00 PM AST on August 27, 2004

...Frances on track...eye getting larger...

interests in the northern Lesser Antilles and the northeastern
Caribbean Sea should closely monitor the progress of Frances over
the next several days.

At 11 PM AST...0300z...the center of Hurricane Frances was located
near latitude 16.3 north... longitude 50.5 west or about 750
miles...1205 km... east of the Leeward Islands.

Frances is moving toward the northwest near 12 mph...19 km/hr. A
motion between northwest and west-northwest is expected for the
next 24 hours or so.

Maximum sustained winds are near 115 mph...185 km/hr...with higher
gusts. Additional strengthening is forecast during the next 24
hours...and Frances could become a category four hurricane over the
weekend.

Hurricane force winds extend outward up to 25 miles... 35 km...
from the center...and tropical storm force winds extend outward up
to 105 miles...165 km.

Estimated minimum central pressure is 962 mb...28.41 inches.

Repeating the 11 PM AST position...16.3 N... 50.5 W. Movement
toward...northwest near 12 mph. Maximum sustained
winds...115 mph. Minimum central pressure... 962 mb.

For storm information specific to your area...please monitor
products issued by your local weather office.

The next advisory will be issued by the National Hurricane Center at
5 am AST.

Forecaster Jarvinen


Hurricane Frances Discussion Number 13

Statement as of 11:00 PM EDT on August 27, 2004

based upon SSMI images and infrared satellite animation...Frances
appears to have gone through an eyewall replacement cycle with the
net result being a larger eye diameter and a likely decrease in
wind speed. This is somewhat confirmed by the fact that TAFB
determined a t5.5 and SAB a t5.0...compared to TAFB having the same
intensity and SAB down one-half T number from 6 hours ago. Global
weather also came in with a t5.0 for this forecast cycle the
initial intensity will remain at 100 kts. Generally...the next
phase after one of these cycles is intensification.

The motion is 310/10. Frances continues moving toward the northwest
and is right on the official forecast track. As mentioned in the
previous discussion...the motion to the northwest is expected to be
short lived as the shortwave trough located due north of Frances
moves eastward and the ridge builds back in behind the trough. This
should turn Frances back to the west-northwest on Saturday. All of
the models now agree that the high zonal flow forecast to develop
across the northern U.S. And the North Atlantic after 48hr will
allow for a strong subtropical ridge to the south to extend
east-west from the Azores to Bermuda and into the southeastern U.S.
The NHC model suite is a little more divergent in the 4 and 5 day
time periods than the previous package...but the consensus model is
almost unchanged. The official forecast for this cycle follows the
previous official out to 72 hours but gently shifts the 4 and 5 day
forecast positions closer to the GUNA positions. This forecast is
also very close to the UKMET solution.

Frances is forecast to remain in a low shear environment and over
increasing SSTs throughout the period. The SHIPS intensity model
continues to keep Frances a major hurricane for the next five days.
There will likely be several fluctuations...as mentioned above...in
the intensity over this period of time...but category four
intensity seems likely some time during that period...and category
5 strength is even possible.

Forecaster Jarvinen

forecast positions and Max winds

initial 28/0300z 16.3n 50.5w 100 kt
12hr VT 28/1200z 17.2n 51.7w 105 kt
24hr VT 29/0000z 18.3n 53.3w 110 kt
36hr VT 29/1200z 19.1n 54.9w 115 kt
48hr VT 30/0000z 19.8n 56.8w 115 kt
72hr VT 31/0000z 20.9n 60.9w 115 kt
96hr VT 01/0000z 22.1n 65.4w 115 kt
120hr VT 02/0000z 23.5n 70.0w 115 kt

[Guest]

interesting update. I also think frances will strengthen.

[Dean4Storms]

I'm seeing some serious warming to the clouds Derek, you could be right about how much she is weakening. Also note the flat look to the western most outflow band, looks to be running into some SW shear to me.

[Hurricanehink]

Wow, I thought it would have been higher.

[canegrl04]

Yep.She wil likely go to cat 4 by Sunday. Watch out for the next eyewal replacement.

[cycloneye]

I thought the movement was 295 in the past 6 hours but 310?

[B-Bear]

So does that basically mean she didn't lose all that much intensity in the eye cycling?

[Air Force Met]

I thought the movement was 295 in the past 6 hours but 310?

That's the overall motion during the last 12 hours and since the last advisory. We will probably see that change to about 295-300 by 5 am if the currrent trend holds. They are always very slow to change a movement...unless they are forecasting it to do so at that time

[~SirCane]

Frances could get scary. :o

[Three Blind Mice]

Wow they even mention possibility of obtaining Cat 5 status!

[wxman57]

So, anyone here still think Dr. Gray should reduce his storm numbers, as many were questioning just 3 weeks ago?