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WxWatcher007

Major Hurricane Florence

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2 minutes ago, Hazey said:

Looks like Flo is hitting her stride. Ramping up quickly now.

Hurricane Florence Tropical Cyclone Update
NWS National Hurricane Center Miami FL       AL062018
835 AM AST Wed Sep 05 2018

...FLORENCE BECOMES A MAJOR HURRICANE...
...FIRST OF THE 2018 ATLANTIC HURRICANE SEASON...

Recent satellite imagery indicates that Florence is still
strengthening and is now a major hurricane.  Maximum sustained
winds are estimated to be 120 mph (195 km/h).  This increase in
intensity will be reflected in the forecast issued with the 1100 AM
AST (1500 UTC) advisory package.


SUMMARY OF 835 AM AST...1235 UTC...INFORMATION
---------------------------------------------------
LOCATION...21.7N 45.2W
ABOUT 1185 MI...1910 KM ENE OF THE NORTHERN LEEWARD ISLANDS
ABOUT 1405 MI...2265 KM ESE OF BERMUDA
MAXIMUM SUSTAINED WINDS...120 MPH...195 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...961 MB...28.38 INCHES

$$
Forecaster Berg/Rhome

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13 minutes ago, SnowGoose69 said:

Wasn’t it the only model at 60 hours last year which had Irma missing MIA and FLL and going into the Keys?  I seem to remember it being heavily discounted and then most of the EPS members in one run jumped way southwest 

That's how I remember it. The rest of the models where pretty consistent at that point, and after watching run after run for days hit somewhere on the East coast, going into the gulf seemed inconceivable. It's a good thing to remember over the next few days, not to get caught up in any potential landfall regions. 

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2 minutes ago, olafminesaw said:

 

Ventrice's tweet seems to be the opposite of what Cowan says

33 minutes ago, BTRWx's Thanks Giving said:

Too bold?

 

 

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Needs to be a few hundred miles south of the GFS track for it to be a serious threat IMO.....there might be 1 or 2 storms ever to get that far north that far east and still threatened the US with a direct landfall.  Though I suppose there is a first time for everything,


Yeah rare for sure.

b63f9a7141f8765a58716b7c4468a337.png


.
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2 minutes ago, yoda said:

Ventrice's tweet seems to be the opposite of what Cowan says

They're talking about two different things. Guidance in the medium and long range has definitely gone west in the past 12 to 18 hours. However short term guidance does have a southwesterly bias. 

 

biaZ (1).png

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25 minutes ago, OSUmetstud said:

They're talking about two different things. Guidance in the medium and long range has definitely gone west in the past 12 to 18 hours. However short term guidance does have a southwesterly bias. 

 

biaZ (1).png

Is this unique to Florence or in general with near term TCs?

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2 minutes ago, hlcater said:

Is this unique to Florence or in general with near term TCs?

This is specifically for Florence. I can't think of a systemic reason why modeling would consistently have a southwest bias with TCs. 

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1 minute ago, OSUmetstud said:

My guess on the bias is mainly because of its intensity being under-modeled. 

Someone somewhere(maybe even here) mentioned that at this point going forward, intensity should affect track less as the cyclone is already vertically deep and is forecast to remain so, and not really decouple. Not discrediting this because this absolutely happened over the past few days because while many models forecast Florence to weaken into a low end TS(or even an open wave!) we now have a major. Just saw someone say that this may have a lesser effect than people would tend to think. Maybe it was CSnavy that said that?

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6 minutes ago, hlcater said:

Someone somewhere(maybe even here) mentioned that at this point going forward, intensity should affect track less as the cyclone is already vertically deep and is forecast to remain so, and not really decouple. Not discrediting this because this absolutely happened over the past few days because while many models forecast Florence to weaken into a low end TS(or even an open wave!) we now have a major. Just saw someone say that this may have a lesser effect than people would tend to think. Maybe it was CSnavy that said that?

Yeah I'm talking about the past. I agree I don't think it's as much of a thing going forward. 

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urricane Florence Discussion Number  25
NWS National Hurricane Center Miami FL       AL062018
1100 AM AST Wed Sep 05 2018

Remarkably, Florence has continued to strengthen.  The hurricane
has a compact central dense overcast with cold cloud tops completely
encircling a clear, well-defined eye.  With the improved structure,
subjective Dvorak estimates have increased to T5.5/102 kt from TAFB
and T6.0/115 kt from SAB, while the latest objective UW-CIMSS ADT
estimate is T5.8/110 kt.  The initial intensity is therefore set at
110 kt as a blend of these numbers, with Florence having become a
major hurricane earlier this morning.

Given the estimated maximum winds, Florence has been rapidly
intensifying since yesterday, an event that was not foreseen by any
intensity models, nor forecasters.  Diagnostics from the SHIPS
model and UW-CIMSS shear analyses have been consistently showing
southwesterly shear of 20-25 kt in the vicinity of Florence, but it
is possible that those schemes are averaging over a larger area
than might be reasonable given the hurricane's small size.  Florence
has apparently been able to find a small pocket of relatively low
shear, and with waters becoming progressively warmer, the hurricane
has strengthened significantly more than anticipated.  This makes
the intensity forecast incredibly uncertain.  SHIPS actually shows
the shear increasing over the next 24 hours, but global model
fields suggest that the hurricane may still be able to continue
within the protected pocket of lower shear for the next several
days.  As a result, the NHC official forecast keeps Florence's
intensity well above the available guidance, which all show the
hurricane weakening over the next day or two.  The new NHC
prediction follows this trend and also shows some weakening, but
this is a low-confidence forecast.  Either way, Florence is
expected to remain a hurricane throughout the 5-day period.

The track forecast also has its challenges.  The initial motion
estimate is northwestward, or 305/11 kt.  It now appears that
stronger upper-level ridging may take shape to the north of
Florence over the next few days, forcing the hurricane to turn back
toward the west-northwest from 36-72 hours.  After 72 hours, a
break in the ridge should allow Florence to turn back toward the
northwest, but the bulk of the track models have trended westward
since yesterday.  In light of these trends, the NHC official track
forecast has been shifted westward on days 4 and 5, but not quite
as far as the various model consensus aids.  It is worth stressing
that there is still a significant amount of spread among the GFS
and ECMWF ensemble members by the end of the forecast period, and
just like the intensity forecast, the track forecast is of low
confidence.


FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z 22.0N  45.7W  110 KT 125 MPH
 12H  06/0000Z 22.7N  47.2W  110 KT 125 MPH
 24H  06/1200Z 23.8N  49.0W  100 KT 115 MPH
 36H  07/0000Z 24.7N  50.6W   95 KT 110 MPH
 48H  07/1200Z 25.1N  52.1W   90 KT 105 MPH
 72H  08/1200Z 25.7N  54.7W   90 KT 105 MPH
 96H  09/1200Z 27.0N  57.0W   95 KT 110 MPH
120H  10/1200Z 28.5N  59.0W   95 KT 110 MPH

$$
Forecaster Berg/Rhome

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12z GFS has Florence getting close to the East Coast... but recurves at the last minute about 500 miles out to sea off OBX

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1 minute ago, yoda said:

12z GFS has Florence getting close to the East Coast... but recurves at the last minute about 500 miles out to sea off OBX

the ukmet and the euro are more more reliable a model to follow then what the gfs says...

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Just now, nycwinter said:

the ukmet and the euro are more more reliable a model to follow then what the gfs says...

I know, just saying what the 12z GFS says for now.  

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I must admit it is awesome seeing a Cape Verde major hurricane. Even though I have no idea of accuracy in percentage since organized maritime tracking increased in the late 1800s, I can't imagine anything less than 99% of tropical storms, much less hurricanes, that pass above 20N45W and miss a CONUS landfall. Certainly nothing like that has occurred in the satellite era. However, I am certain that it has happened multiple times if we had a thousand years of tracking to observe. Regardless, the atmospheric pattern and outright luck for the TC to be steered through to landfall is exceedingly a rarest phenomenon to occur in modern meteorology, so count me fascinated. And why my confidence has to remain low of a CONUS landfall even if weakening back down to a C1/TS is imminent with regards to the lower steering layer.

As for how Florence's stronger intensity has been achieved and how delicate: The 200 mb WSW flow looks to have assisted in strong ventilation to the ENE of Florence. Also, and this is speculation on my part, but Florence does not have much in the way of outter banding and has a core ring with minimal outter convection. The TC's vortex structure combined with cooler than mean upper trop temps may be assisting in driving low-level instability over marginal 27°C SSTs. At any rate, Florence is definitely hitting MPI. The axis of slightly deeper layer 400-300 mb westerly flow is still nearby and bending around Florence's position perfectly at the moment. Not sure how long current TC intensity will last but any minute change towards Florence's core should weaken the TC dramatically.

b90182f77d36f7d4492b105b5a771284.jpg

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4 minutes ago, yoda said:

12z GFS has Florence getting close to the East Coast... but recurves at the last minute about 500 miles out to sea off OBX

Novice here ,, my understanding is the GFS is not as reliable with Hurricanes as say the Euro and Ukie. Can someone explain how a novice  like myself can tell or see  where the shear or Ridge is actually setting up or happening ? Thanks in advance

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Storms with persistent convection in the downshear left region of the core can fight off light to moderate shear. I saw this in a paper somewhere but I cant find it now cause I'm on my phone at work.

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Anyone else notice that the latest GFS and Canadian models maintain a bit of a dip in 500 mb heights over the Ohio/Tennessee valley region as Florence approaches, which doesn't allow the ridging to the north of Florence to extend as far west as it does on the Euro.  Of course, this is so far down the road that plenty of details will change.

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12z UK is pretty far south with the track, moving west at 144 hrs along Miami's latitude, but it's also way too weak with the low for the first few days and actually shows it moving wsw for a day after 72 hrs.

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48 minutes ago, Coach McGuirk said:

Looking really nice on satellite, how did they get the intensity so wrong? 

It's not totally clear, but from the NHC's discussion and some satellite interp, it looks like it has been sitting couched in a pocket of lower shear. This wasn't expected. Also, despite the marginal SSTs, it has maintained a decent (but not too fast) forward motion, keeping it from significantly upwelling the ocean underneath and allowing it to feed off the upper MLD waters.

I'm sure the favorable outflow pattern aloft is helping as well.

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25 minutes ago, hawkeye_wx said:

Anyone else notice that the latest GFS and Canadian models maintain a bit of a dip in 500 mb heights over the Ohio/Tennessee valley region as Florence approaches, which doesn't allow the ridging to the north of Florence to extend as far west as it does on the Euro.  Of course, this is so far down the road that plenty of details will change.

The problem on the GFS appears to be the departing trough near the Labrador Sea. The trough helps to knock down the ridge over the Atlantic and force it East, so the flow becomes more Northwesterly rather than Westerly. This has large implications because both the GFS and ECMWF develop another ridge near Bermuda, and with Florence on the Western side, the system becomes enveloped in the Northerly and eventually Northeasterly flow thanks to the clockwise rotation around the high.

gfs_z500_mslp_atl_30.png

gfs_uv200_atl_30.png

The Euro is much weaker with the trough, therefore the ridge over the Atlantic is able to stand its ground longer. The flow remains more Westerly and eventually Florence ends up being forced into the coast by the second ridge over Quebec.

ecmwf_z500_mslp_atl_8.png

ecmwf_z500_mslp_atl_9.png

So in the grand scheme of things, nothing much has changed. We still need to see how the short term uptick in intensity ultimately influences the track. While it's true that a deeper system would feel the weakness more, the models almost unanimously have trended weaker with that feature, and my confidence is increasing that Florence will miss the initial trough.

We will have to see how models trend in terms of amplitude of the second trough. 

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In terms of a threat area along the East coast, it's really too early to rule out any particular location.

Someone posted about the UKMET showing a SW movement later in the period and that is certainly possible if the ridge ends up as strong as the Euro and UKMET shows. It's really not that unusual.

Andrew actually tracked WSW on approach to the Bahamas.

I would think the main threat area however is from about Charleston to Nova Scotia, with the greatest threat from OBX to Montauk Point. I don't like how the trajectory of this system would most likely be from the SE rather than the South.

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watching and analyzing every single operational run is fairly pointless this far out. keep an eye on the ensembles and overall trends.

i think the best forecasting tool right now is the observed bias for the west atlantic ridge to be weakened too soon in the extended period. assuming that ridge will be longer-lived and more robust than modeled - especially on the GFS - has been useful going back through last winter.

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