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6Sept18 5pEDT/AST - Estimated winds 80mph(130km/h), moving NW 10mph(17km/h), pressure 989mb. Barely a Cat1 now. May drop below Hurricane strength but by the weekend shear tearing it apart begins to subside and warm waters of the Atlantic await so expected to start restrengthening eventually. From NHC Discussion page: "It is important to note that deterministic track models in these types of situations often display considerable run-to-run changes, and the uncertainty in this forecast remains larger than normal."
Been in hurricane country a long time. Never ever seen that dramatic of a change that quickly.
Shear in that area has been 25-30 knots, which is super high. It's actually been more of a surprise to forecasters that Flo increased as much as she did considering her environment. Although if you read over the NHC discussions on the storm over the last couple of days they gave some reasons why: very small storm (which ramp up and down faster than larger storms) that found a micro-zone of lower shear within the overall macro area. Also, there's a whole lot of dry air to Flo's south.
How is it possible to go from a Cat 4 to a tropical storm in 24 hours?
Good conditions for intensification to sudden, non-gradual, not so great conditions, mainly very high wind shear in this case. There are other weather systems nearby but I don't know enough to comment on potential interactions if they also helped or not the weakening in this case. But this is also estimated winds since aircraft recon won't be there to measure actual until Monday.
But in trying to find records I did see this is the second fastest weakening storm on record in a 24hour period at least for South of 30°N & East of 60°W (see the cone map to see what that area is). I'm sure its up there in other regions too but easier to find data on strengthening storms then weakening ones.
Thia is true...I think. Would really have to dig in archives to check but given how unprecedented this humidity is we are experiencing in the Northeast it tells us this setup isnt usual. A strong blocking this far north with a major hurricane underneath it is not something we usually see...or models understand for that matter.
His reply "Simple terms: There is a very unusually strong ridge forecast to be to the north of Florence. This creates a much more concerning setup - typically, a storm in Florence’s position would likely curve out to sea. But this setup is not typical."
UPDATE: Florence weakens even more but don't let your guard down.
Quote:
NWS National Hurricane Center Miami FL AL062018
500 AM AST Fri Sep 07 2018
...FLORENCE WEAKENS A LITTLE MORE BUT STILL EXPECTED TO
RESTRENGTHEN OVER THE WEEKEND...
SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...25.1N 50.7W
ABOUT 925 MI...1490 KM ENE OF THE NORTHERN LEEWARD ISLANDS
ABOUT 985 MI...1590 KM ESE OF BERMUDA
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...W OR 275 DEGREES AT 7 MPH...11 KM/H
MINIMUM CENTRAL PRESSURE...996 MB...29.42 INCHES
DISCUSSION AND OUTLOOK
----------------------
At 500 AM AST (0900 UTC), the center of Tropical Storm Florence was
located near latitude 25.1 North, longitude 50.7 West. Florence is
moving toward the west near 7 mph (11 km/h). This general motion
will likely continue for the next couple of days. A turn toward
the west-northwest is expected by the end of the weekend.
Maximum sustained winds have decreased to near 65 mph (100 km/h)
with higher gusts. Little change in intensity is expected today.
However, Florence is forecast to restrengthen and become a hurricane
again over the weekend.
Tropical-storm-force winds extend outward up to 140 miles (220 km)
from the center.
The estimated minimum central pressure is 996 mb (29.42 inches).
This weekend I may start saying Carolinas need to have a plan in place if this continues.
Latest Euro00z hits SC/NC border Thursday. Only 6 days away now
Detailed Discussion: When cloud tops warm its a sign of weakening but shear is at its peak now so strengthening should be happening soon. Important note in red!! 20 miles not a lot but its south more which gives it an even better chance at hitting U.S
Quote:
Tropical Storm Florence Discussion Number 32
NWS National Hurricane Center Miami FL AL062018
500 AM AST Fri Sep 07 2018
Florence's structure continues to be negatively affected by strong
southwesterly shear. Cloud tops have generally warmed over the
past 6 hours, and recent microwave data show that the low-level
circulation center of Florence is displaced nearly 20 nmi to the
southwest of the mid-level center. Satellite intensity estimates
have decreased since last night, and now support an initial
intensity of 55 kt.
Based on GFS and ECMWF SHIPS diagnostic output, the southwesterly
shear is near its peak now, and should gradually decrease over the
next 24 to 36 h. All of the intensity guidance shows little change
in intensity through that time. From 48 h onward, a low shear/warm
SST environment should allow the tropical storm to re-strengthen.
However, the extent and timing of the strengthening varies greatly
from model to model, with the dynamical models generally showing
more intensification, and sooner, than the statistical models. As
has been the case for most of Florence's existence thus far,
confidence in the intensity forecast, especially beyond 36 h, is
low. The new official forecast is a little lower than the previous
advisory for the first 48 h, but close to it after that, and lies
between the more aggressive HCCA and less aggressive IVCN consensus
aids.
Nighttime Proxy-Vis and earlier microwave imagery indicate that
Florence has turned westward, with an estimated initial motion of
275/6 kt. Most of the track guidance has shifted slightly toward the
southwest, so the NHC track forecast has also been nudged in that
direction. Over the next 3 days of the forecast, Florence should be
steered generally westward, and then west-northwestward, by a
mid-level ridge to its north. By days 4 and 5, a developing
mid-latitude trough could create a weakness in this ridge and allow
Florence to move more toward the northwest, but there is still
considerable uncertainty in the global models and their ensembles
regarding the strength of the ridge and if the aforementioned trough
will have any notable impact on the track of Florence. The NHC
forecast follows HCCA very closely, and is also near the middle of
the large combined envelope of the GFS, UKMET, and ECMWF ensembles.
Key Messages:
1. Regardless of Florence's eventual track, large swells will begin
to affect Bermuda later today and portions of the U.S. East Coast
this weekend, resulting in life-threatening surf and rip currents.
2. There is still very large uncertainty in Florence's track
beyond day 5, and it is too soon to determine what, if any, other
impacts Florence could have on the U.S. East Coast next week.
3. Since we are near the peak of hurricane season, this is a good
time for everyone who lives in a hurricane-prone area to ensure they
have their hurricane plan in place
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