Frances Advisories

[c5Camille]

agreed...

[Wthrman13]

Thanks Brent! I have actually noticed that storms seem to burst at around 10pm and then again they spurt at around 3 am and then level off or even die down again once the sun rises and the daytime heating begins. -seems like the opposite should happen if these things ar esupposed to feed on heat.

The reason convection over oceans often is enhanced at night is because of cloud top radiational cooling. The clouds emit infrared energy into space, causing them and the air immediately above them to cool off. Since the ocean surface temperatures don't change all that much from day to night, due to the high heat capacity of water, This steepens the temperature gradient between the cloud top and surface, causing the atmosphere to be more unstable and contributing to the enhanced convection.

The reason you typically see convection die off at night over land areas is that the land surface cools off much quicker than a water surface. You still have the effects of cloud top radiational cooling over land, but they are offset by the simultaneous cooling of the land, so the temperature gradient actually tends to reverse sign at night, especially near the surface. That is, the temperature actually increases with height in the low levels, being coldest near the cool surface, which is a very stable situation that suppresses convection.

So, there are basically two ways to destabilize a layer of the atmosphere. Either warm the bottom (as in solar heating of a land surface), or cool off the top (as in cloud top radiational cooling). Both have the effect of enhancing the chances and strength of convection.

[Guest]

i agree 100% with you. I think it will be a cat 2 with an eye by morning.

[ColdFront77]

Oops! Sorry hon, that post came across as if I sounded mad! I was echoing your words, not arguing or making any nasty comment. More like..."hell yeah! I hear that! -after what I just went through..." haha.

My grandmother lives in Altamonte Springs and her area got pretty tore up from Charley's crossing. Here on my island, we didn't even see a breeze stronger than our daily seabreeze from Charley!

I thought you came across as sounded mad at first, so it came out that way in my posts. My apologizes for my response, too. It's all good. Thanks!

[TreasureIslandFLGal]

Wow! Great explanation! Thanks on behalf of a few of us that I'm sure just learned something!

[WXBUFFJIM]

I couldn't agree more. Outflow is very good in all quadrants and the CDO is becoming better established. Also notice the sinking air around the outskirts of this system, once again evidence of better outflow, hence we'll only see further strengthening through the next 36-48 hours and possibly beyond that.

A major hurricane by Friday evening into early Saturday is a definite possibility.

Jim

[x-y-no]

Agreed - it's looking stronger.

And after the northwesterly wobble earlier, it's now wobbling the other way almost due west. I'd say the average is WNW.

[schmita]

Yeah, and we are at 18 N and 63 W. The new LBAR has it right on top of us in 120 hrs. I know that's far out but still......irina

[mb229]

Wthrman13 .....Thanks for the very clear explanation of enhanced clound convection at night.

Hello to all who have made this board a great place to lurk for a couple of years!

I am a storm nut...Donna, Fran, Floyd, and many NC approaches have made me this way.

[Lowpressure]

Watch to see if a comparison to Isabel becomes relevent in regards to strength and subsequent path.

[vbhoutex]

The stronger the storm the more it will feel the weakness in the ridge. However, so far the weakness being produced by the incoming trough and ULL is not very noticeable and the trough appears to be lifting out quickly so it's effects will apparently not be major on the overall course even though we will probably see a zig or zag more NW for a short time before the ridge fills back in and pushes Frances to a more WNW or West course.

The front in Denver is probably not going to have any effect on Frances since it should be off the East Coast and gone before Frances gets close enough to feel the trough that would be associated with it. Our locals OCM's in Houston are not even thinking it will make it all the way through here so it is not that strong of a front either. Now whatever comes in next behind the front you are talking about could be a player in the scenario if it is strong enough. As always with the tropics, we wait and watch and prognosticate, and Mother Nature does what she wants too.

[WXBUFFJIM]

Hope for the best for St. Maarten, that's for sure.

[dhweather]

Ahhhh, Hurricane Frances, well, she'll give us lots to talk about over
the next several days.

[dhweather]

Conditions certainly appear favorable for quick intensification.
Maybe a cat 2/3 by 10PM CST tomorrow.

[Anonymous]

Is forecast to get to 120 mph... and that is conservative.... this will not be a friendly week from mother nature.

[Wnghs2007]

Hurricane Frances Discussion Number 8


Statement as of 5:00 PM EDT on August 26, 2004



Frances has continued to become better organized with a small 10-15
nmi diameter banding eye feature occasionally appearing. Satellite
intensity is t4.0...or 65 kt...from both TAFB and SAB...and the
trend of going slightly higher than the satellite estimates are
indicating is being continued on this advisory. Upper-level outflow
is good to excellent in all quadrants and continues to improve.

The initial motion is 295/14. Frances has remained on track and the
majority of the NHC model guidance is in much better agreement now
...Except for the NOGAPS model...which appears to be a sharp
right-of-track outlier. In fact...the latest UKMET run has shifted
much farther west while the GFS has shifted a little to the right.
Those two models...plus the GFDL...have now converged on top of the
previous forecast track through 72 hours and then only diverge
slightly away from the 12z track after that. Water vapor imagery
suggests the Canadian Maritimes low appears to have bottomed out
and is shifting slowly eastward...so only a slight weakening of the
subtropical ridge to the north of Frances is expected in the 36-72h
time period. Afterwards...all of the global models...even NOGAPS...
is forecasting the mid-latitude flow across the northern U.S. And
the North Atlantic to become strongly zonal. With such strong
westerly high-latitude flow becoming established...a corresponding
response should be a strengthening of the Bermuda-Azores ridge
westward to perhaps the U.S. East Coast by 120 hours. That pattern
should help to turn Frances more westward after 96 hours. As such
...The forecast track is just an extension of the previous track.
Since Frances appears to have mixed out any dry air intrusions...has
a rather small eye...and good outflow established...then additional
rapid intensification seems likely for at least another 12 hours or
so. After that...the intensification trend is leveled since at
least one concentric eyewall cycle should occur in the next 72
hours due to the current small diameter eye. Timing any additional
eyewall cycles with any kind of skill just is not possible...but
some additional strengthening may still occur since the hurricane
will be passing over 29c SSTs...about 1c above average...by 96hr.
The intensity forecast is a blend of the SHIPS and GFDL models.
Forecaster Stewart

forecast positions and Max winds

initial 26/2100z 13.7n 46.4w 70 kt
12hr VT 27/0600z 14.6n 48.1w 85 kt
24hr VT 27/1800z 15.8n 50.2w 95 kt
36hr VT 28/0600z 16.9n 51.7w 100 kt
48hr VT 28/1800z 17.8n 52.8w 100 kt
72hr VT 29/1800z 19.0n 55.0w 105 kt
96hr VT 30/1800z 20.5n 58.5w 105 kt
120hr VT 31/1800z 21.5n 62.5w 105 kt


$$

[msbee]

gonna be a close call

[WXBUFFJIM]

Definitely not real shocking at all to see this raised to a strong category 1 given the satellite appearance. With each passing hour, satellite presnetations get better and better. Only obstacle is thge eyewall replacement cycles. But that's about the only small hindering factor and even that could be just a temporary issue.

Jim

[WXBUFFJIM]

The bottom line is it's forecast to become a major hurricane, which is definitely something to consider.

[Guest]

Seems to me like Frances is going to really get powerful next day or 2. especially with the +1c abv water ssts