ATL: FLORENCE - Advisories

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cycloneye
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Re: ATL: FLORENCE - Advisories

#21 Postby cycloneye » Sun Sep 02, 2018 9:36 pm

BULLETIN
Tropical Storm Florence Advisory Number 15
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Sun Sep 02 2018

...FLORENCE CONTINUES TO HOLD STEADY IN STRENGTH OVER THE EASTERN
ATLANTIC...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...17.9N 35.9W
ABOUT 790 MI...1275 KM WNW OF THE SOUTHERNMOST CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...1000 MB...29.53 INCHES




Tropical Storm Florence Discussion Number 15
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Sun Sep 02 2018

Florence has generally changed little during the past several
hours. The cloud pattern consists of a central dense overcast
feature with the low-level center estimated to be closer to the
southern side of the convection. All of the satellite intensity
estimates have held steady and support maintaining the wind speed
at 45 kt.

Although Florence is located in an environment of relatively low
wind shear, the SSTs beneath the cyclone are cool, around 26 deg C.
The tropical storm is expected to move over gradually warmer waters
beginning in about 24 hours, but it will also be moving into an
environment of higher shear. These mixed signals suggest that
Florence will likely change little in intensity or weaken
slightly during the next few days. By the end of the forecast
period, however, the shear is expected to lessen and by then
Florence should be over much warmer waters. Therefore,
strengthening seems likely in the 4 to 5 day time period. The NHC
intensity forecast is a little lower than the previous one to come
into better agreement with the latest guidance.

Florence is moving west-northwestward at 15 kt steered by a
mid-level ridge to its northeast. Although the track models all
show a west-northwestward to northwestward motion during
the next several days, the north-south spread becomes fairly large
by the end of the forecast period. This spread appears to be
primarily associated with differences on how strong or vertically
coherent each model predicts Florence to be. Since the NHC forecast
shows the storm changing little in strength for the next few days,
this track prediction lies near the middle of the guidance envelope
close to the various consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 03/0300Z 17.9N 35.9W 45 KT 50 MPH
12H 03/1200Z 18.3N 38.1W 45 KT 50 MPH
24H 04/0000Z 18.7N 40.6W 45 KT 50 MPH
36H 04/1200Z 19.2N 43.0W 45 KT 50 MPH
48H 05/0000Z 19.8N 45.2W 45 KT 50 MPH
72H 06/0000Z 21.5N 49.6W 40 KT 45 MPH
96H 07/0000Z 23.6N 53.8W 40 KT 45 MPH
120H 08/0000Z 25.5N 56.7W 50 KT 60 MPH

$$
Forecaster Cangialosi
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Re: ATL: FLORENCE - Advisories

#22 Postby cycloneye » Mon Sep 03, 2018 5:01 am

BULLETIN
Tropical Storm Florence Advisory Number 16
NWS National Hurricane Center Miami FL AL062018
500 AM AST Mon Sep 03 2018

...FLORENCE CONTINUES WEST-NORTHWESTWARD...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...18.0N 37.5W
ABOUT 895 MI...1440 KM WNW OF THE SOUTHERNMOST CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...60 MPH...95 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES



Tropical Storm Florence Discussion Number 16
NWS National Hurricane Center Miami FL AL062018
500 AM AST Mon Sep 03 2018

The structure of Florence has recovered overnight. Several recent
microwave images indicate that the tropical storm's center is still
dislocated to the south of most of the associated convection, but
convective banding has increased. There is also evidence that
Florence has developed better defined low-level inner-core.
Satellite intensity estimates have increased and now range from 45
to 60 kt. As a compromise of the various estimates, the initial
intensity has been raised slightly to 50 kt, but its worth noting
that this increase is within the noise level of our ability to
observe the intensity of tropical storms over the open ocean.

Based on SHIPS diagnostics, the southwesterly shear affecting
Florence could remain moderate for the next 12 h, and some slight
intensification is possible. However, by 24 h, an increase in the
shear should kick off a gradual weakening trend. By the end of the
forecast period, the tropical storm is forecast to re-intensify
while it moves over warmer SSTs and the environmental shear
decreases. Given the improved current structure of Florence, the new
official intensity forecast shows slight intensification for the
first 12 h. Beyond that time, the models are in good agreement and
the NHC forecast is near the middle of the relatively tight
intensity guidance envelope.

The tropical storm is still moving west-northwestward, at an
estimated 14 kt. A continued west to west-northwest motion is
forecast by all the global models for the next couple of days. By
the end of the forecast period, nearly all of the guidance shows a
turn toward the northwest, and the main source of uncertainty in
the track forecast continues to be exactly when and to what extent
Florence will make this turn. At this point I have no reason to
depart from the various consensus models, and the track forecast is
very close to the previous advisory.

FORECAST POSITIONS AND MAX WINDS

INIT 03/0900Z 18.0N 37.5W 50 KT 60 MPH
12H 03/1800Z 18.3N 39.6W 55 KT 65 MPH
24H 04/0600Z 18.7N 42.0W 50 KT 60 MPH
36H 04/1800Z 19.3N 44.2W 45 KT 50 MPH
48H 05/0600Z 20.0N 46.5W 45 KT 50 MPH
72H 06/0600Z 22.2N 51.1W 40 KT 45 MPH
96H 07/0600Z 24.5N 54.5W 45 KT 50 MPH
120H 08/0600Z 26.0N 57.0W 55 KT 65 MPH

$$
Forecaster Zelinsky
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Re: ATL: FLORENCE - Advisories

#23 Postby cycloneye » Mon Sep 03, 2018 9:44 am

BULLETIN
Tropical Storm Florence Advisory Number 17
NWS National Hurricane Center Miami FL AL062018
1100 AM AST Mon Sep 03 2018

...FLORENCE A LITTLE STRONGER AS IT CONTINUES MOVING ACROSS THE
CENTRAL TROPICAL ATLANTIC...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...18.3N 38.7W
ABOUT 980 MI...1580 KM W OF THE CABO VERDE ISLANDS
ABOUT 1505 MI...2425 KM E OF THE LESSER ANTILLES
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...997 MB...29.44 INCHES



Tropical Storm Florence Discussion Number 17
NWS National Hurricane Center Miami FL AL062018
1100 AM AST Mon Sep 03 2018

While Florence's structure improved overnight, the cloud tops have
warmed and the deep convection has thinned during the past several
hours. The 12Z satellite intensity estimates range from 55 to 65 kt,
but given recent trends the initial intensity is set at the low end
of that range at 55 kt, although this is quite uncertain given the
recent fluctuations in the cloud pattern.

UW-CIMSS satellite diagnostics indicate that around 20 kt of
southwesterly shear is affecting Florence, while the SHIPS analysis
based on the GFS fields shows only about 10 kt. SSTs warm from this
point forward along the forecast track, but shear is expected to
be steady or strengthen, and the mid-level relative humidity values
decrease to around 50 percent during the next 48 to 72 hours. Given
these mixed factors, the NHC intensity forecast shows some
possibility for strengthening in the next 12 hours, followed by a
slow decay through 72 hours. Some restrengthening is forecast late
in the period as SSTs warm above 28C and the atmospheric moisture
increases. The NHC forecast is close to or a bit above the latest
IVCN consensus aid and about 5 kt above the previous NHC forecast
through 96 hours.

The initial motion estimate is 285/14. Florence will be steered
generally west-northwestward for the next 72 hours by the Atlantic
subtropical ridge, followed by a northwestward turn at days 4 and 5.
While there is large spread in the guidance between the HWRF on the
right and the UKMET on the left, the GFS, ECMWF, and their ensemble
means are more tightly clustered near the middle of the guidance
envelope. Since the overall track forecast reasoning has not
changed, the new NHC forecast remains near the middle of the
guidance. This forecast is a bit north of the previous NHC track
given the initial position and lies a little south of the consensus
aids to reflect less influence of the outlier HWRF model to the
north.

FORECAST POSITIONS AND MAX WINDS

INIT 03/1500Z 18.3N 38.7W 55 KT 65 MPH
12H 04/0000Z 18.6N 40.7W 60 KT 70 MPH
24H 04/1200Z 19.1N 43.0W 60 KT 70 MPH
36H 05/0000Z 19.9N 45.3W 55 KT 65 MPH
48H 05/1200Z 20.8N 47.6W 50 KT 60 MPH
72H 06/1200Z 23.0N 52.2W 45 KT 50 MPH
96H 07/1200Z 25.0N 55.0W 50 KT 60 MPH
120H 08/1200Z 27.0N 58.0W 55 KT 65 MPH

$$
Forecaster Brennan
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Re: ATL: FLORENCE - Advisories

#24 Postby cycloneye » Mon Sep 03, 2018 3:33 pm

BULLETIN
Tropical Storm Florence Advisory Number 18
NWS National Hurricane Center Miami FL AL062018
500 PM AST Mon Sep 03 2018

...FLORENCE JUST BELOW HURRICANE STRENGTH...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...18.6N 39.8W
ABOUT 1055 MI...1700 KM WNW OF THE CABO VERDE ISLANDS
ABOUT 1435 MI...2310 KM ENE OF THE LESSER ANTILLES
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...995 MB...29.39 INCHES


TAA00 KNHC DDHHMM

Tropical Storm Florence Discussion Number 18
NWS National Hurricane Center Miami FL AL062018
500 PM AST Mon Sep 03 2018

Florence appears a little better organized than earlier today. Deep
convection is slightly stronger near and to the north of the center,
and the cloud pattern still resembles a central dense overcast. A
blend of the latest Dvorak classifications suggests a slightly
higher wind speed, and accordingly, the initial intensity is nudged
upward to 60 kt.

The strong tropical storm is moving westward, or 280 degrees, at 13
kt steered by a subtropical ridge to its north. The global models
all show a persistent weakness in the subtropical ridge during the
next several days due to a series of troughs moving across the
Atlantic. In response, Florence is expected to gradually turn
northwestward with a slight reduction in forward speed during the
next several days. While there remains a fair amount of spread in
the models from 72 to 120 h, there has been a notable trend to the
right, or north, during the past few model cycles. The official
track forecast is adjusted slightly to the right as well, trending
toward the latest consensus aids.

Little change in strength is expected through tonight as Florence
remains over marginally warm waters and in moderate wind shear
conditions. However, nearly all of the intensity models show a slow
weakening trend during the next few days. This weakening is in
response to a gradual increase in southwesterly or westerly shear.
Beyond a few days, however, the shear is expected to decrease and
Florence will be over much warmer waters. Therefore, slow
strengthening is shown in the 3 to 5 day period. This forecast is
slightly higher than the previous one at the longer range, but is
otherwise unchanged.

FORECAST POSITIONS AND MAX WINDS

INIT 03/2100Z 18.6N 39.8W 60 KT 70 MPH
12H 04/0600Z 19.0N 41.6W 60 KT 70 MPH
24H 04/1800Z 19.6N 43.9W 55 KT 65 MPH
36H 05/0600Z 20.4N 46.1W 55 KT 65 MPH
48H 05/1800Z 21.5N 48.4W 50 KT 60 MPH
72H 06/1800Z 23.7N 52.5W 50 KT 60 MPH
96H 07/1800Z 26.0N 55.3W 55 KT 65 MPH
120H 08/1800Z 28.0N 57.5W 60 KT 70 MPH

$$
Forecaster Cangialosi
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Re: ATL: FLORENCE - Advisories

#25 Postby cycloneye » Mon Sep 03, 2018 9:38 pm

Tropical Storm Florence Discussion Number 19
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Mon Sep 03 2018

Although Florence continues to produce a fairly circular area of
deep convection, microwave images have revealed that there is a
significant southwest-to-northeast vertical tilt of the
circulation due to southwesterly shear. The initial intensity is
held at 60 kt, using a blend of the Dvorak CI-numbers from TAFB and
SAB. This estimate is a little below the latest automated Dvorak
values from CIMSS at the University of Wisconsin.

The strong tropical storm is moving west-northwestward, or 285
degrees, at 12 kt steered by a subtropical ridge to its north. The
storm is expected to gradually turn northwestward with a decrease
in forward speed during the next several days as it moves
toward a persistent weakness in the subtropical ridge. There
remains a fair amount of spread in the guidance, especially in the
3- to 5-day time period, but the consensus aids have changed little
this cycle. Therefore, no significant changes were made to the
previous forecast, and this one lies near the middle of the guidance
envelope.

Little change in strength is expected through early Tuesday as
Florence remains over marginally warm waters and in moderate wind
shear conditions. Slight weakening is expected during the middle
part of the week due to a gradual increase in southwesterly or
westerly shear. Beyond that time, however, the shear is expected to
decrease and Florence will be over much warmer waters. Therefore,
slow strengthening is shown at the end of the forecast period.
This forecast is unchanged from the previous one, and is in good
agreement with the HCCA guidance.

The 34- and 50-kt initial wind radii have been expanded outward
based on recent ASCAT passes.

FORECAST POSITIONS AND MAX WINDS

INIT 04/0300Z 18.9N 41.0W 60 KT 70 MPH
12H 04/1200Z 19.4N 42.7W 60 KT 70 MPH
24H 05/0000Z 20.1N 44.9W 55 KT 65 MPH
36H 05/1200Z 21.1N 47.2W 55 KT 65 MPH
48H 06/0000Z 22.1N 49.5W 50 KT 60 MPH
72H 07/0000Z 24.5N 53.1W 50 KT 60 MPH
96H 08/0000Z 26.8N 55.8W 55 KT 65 MPH
120H 09/0000Z 28.4N 57.8W 60 KT 70 MPH

$$
Forecaster Cangialosi
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Re: ATL: FLORENCE - Advisories

#26 Postby cycloneye » Tue Sep 04, 2018 5:34 am

Tropical Storm Florence Discussion Number 20
NWS National Hurricane Center Miami FL AL062018
500 AM AST Tue Sep 04 2018

Florence's cloud pattern has changed very little during the past
several hours, with the exception of a possible small Central Dense
Overcast developing just to the east of the center. An earlier
AMSR2 overpass revealed a rather obvious tilt toward the
east-northeast, indicative of the moderate southwesterly shear.
The initial intensity is held a 60 kt, and is supported by the
Dvorak subjective and objective T-numbers.

Florence should exhibit little change in strength during the next
24 hours or so, as the cyclone traverses marginally warm sea surface
temperatures and is influenced by modest west-southwesterly shear.
Slight weakening is expected during the mid- forecast period as the
shear gradually increases with time. Afterward, the upper-level
wind environment should become a little more favorable and, at the
same time, Florence will be moving back over warmer SSTs.
Consequently, the cyclone should gradually strengthen through day 5.
This forecast is unchanged from the previous one, and is in good
agreement with the NOAA-HCCA guidance.

The initial motion estimate is west-northwestward, or 290/11 kt.
The cyclone is expected to be steered west-northwestward for the
next 48 hours by a mid- to upper tropospheric ridge anchored to
the north, followed by a northwestward turn around the 72 hr period
as it enters a growing weakness in the aforementioned ridge. A
rather large spread in the global and hurricane models remains
particularly beyond day 4, however, the consensus models and the
global ensemble means have have been fairly consistent from run to
run. This forecast is just a bit to the north of the previous
advisory and just south of the consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 04/0900Z 19.3N 42.0W 60 KT 70 MPH
12H 04/1800Z 19.9N 43.7W 60 KT 70 MPH
24H 05/0600Z 20.8N 45.8W 60 KT 70 MPH
36H 05/1800Z 21.8N 48.0W 55 KT 65 MPH
48H 06/0600Z 22.9N 50.2W 50 KT 60 MPH
72H 07/0600Z 25.2N 53.4W 50 KT 60 MPH
96H 08/0600Z 27.1N 55.6W 55 KT 65 MPH
120H 09/0600Z 29.1N 57.7W 65 KT 75 MPH

$$
Forecaster Roberts
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Re: ATL: FLORENCE - Advisories

#27 Postby cycloneye » Tue Sep 04, 2018 9:41 am

Hurricane Florence Discussion Number 21
NWS National Hurricane Center Miami FL AL062018
1100 AM AST Tue Sep 04 2018

Florence's structure has gradually increased in organization, with
SSMIS passes from a few hours ago revealing the development of a
mid-level microwave eye. Dvorak estimates have responded in
kind--TAFB is up to T4.0, SAB is at T4.5, and the objective ADT is
in between at T4.4. Since there still appears to be moderate
southwesterly shear inducing some tilt to the cyclone and
disrupting the infrared satellite pattern, the initial intensity is
raised conservatively to 65 kt, making Florence a hurricane.

The current motion remains west-northwestward, or 295/10 kt, with
Florence positioned near the southwestern edge of the subtropical
ridge. The steering pattern ahead of Florence is rather complicated
and will be evolving over the next few days. A large and complex
mid-/upper-level trough located northeast of the Leeward Islands is
expected to give way to the development of two upper-level highs
centered near the Greater Antilles and southwest of the Azores, with
Florence slowing down and turning northwestward between these new
features. Despite this complex pattern, the spread in the track
models is less than normal, which increases the confidence in the
NHC track forecast for the next 5 days. There is some spread which
begins to develop around day 5, with the ECMWF model moving Florence
a little faster toward the north while the GFS maintains a slower
speed and keeps the system to the south. The updated NHC track
forecast has been nudged slightly to the east of the previous
forecast on days 4 and 5, close to the TVCX consensus but not as far
as the HCCA and ECMWF models. There is still too much model spread
after day 5 to speculate what Florence might do beyond the official
forecast period.

Despite Florence becoming a hurricane, the southwesterly shear
affecting the cyclone is expected to increase over the next day or
two, which should prevent further intensification. In fact, the
increasing shear, as well as mid-level relative humidities below 50
percent, should cause weakening between 24 and 72 hours. After 72
hours, decreasing shear and warmer sea surface temperatures should
foster some re-intensification, with Florence expected to reattain
hurricane intensity by day 5. The intensity guidance is in good
agreement, and the NHC forecast is very close to a blend of HCCA,
the Florida State Superensemble, and the ICON consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 04/1500Z 19.7N 42.5W 65 KT 75 MPH
12H 05/0000Z 20.3N 44.0W 65 KT 75 MPH
24H 05/1200Z 21.3N 46.2W 65 KT 75 MPH
36H 06/0000Z 22.4N 48.2W 60 KT 70 MPH
48H 06/1200Z 23.6N 50.0W 55 KT 65 MPH
72H 07/1200Z 25.6N 52.7W 50 KT 60 MPH
96H 08/1200Z 27.5N 55.0W 55 KT 65 MPH
120H 09/1200Z 29.5N 56.5W 65 KT 75 MPH

$$
Forecaster Berg
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Re: ATL: FLORENCE - Advisories

#28 Postby cycloneye » Tue Sep 04, 2018 2:31 pm

Hurricane Florence Tropical Cyclone Update
NWS National Hurricane Center Miami FL AL062018
250 PM AST Tue Sep 04 2018

...FLORENCE CONTINUING TO STRENGTHEN...

Recent satellite imagery indicates that Florence has continued to
intensify during the past few hours, and maximum sustained winds
have increased to 85 mph (140 km/h). This increase in intensity
will be reflected in the forecast issued with the 500 PM AST (2100
UTC) advisory package.


SUMMARY OF 250 PM AST...1850 UTC...INFORMATION
---------------------------------------------------
LOCATION...20.0N 42.7W
ABOUT 1265 MI...2035 KM ENE OF THE LESSER ANTILLES
MAXIMUM SUSTAINED WINDS...85 MPH...140 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...984 MB...29.06 INCHES

$$
Forecaster Brennan/Berg
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Re: ATL: FLORENCE - Advisories

#29 Postby cycloneye » Tue Sep 04, 2018 3:36 pm

Hurricane Florence Discussion Number 22
NWS National Hurricane Center Miami FL AL062018
500 PM AST Tue Sep 04 2018

Despite being over marginally warm water and in an environment of
moderate west-southwesterly shear, Florence's intensity has
increased during the day. The hurricane has a cloud-filled eye in
visible imagery, and the central dense overcast is becoming more
symmetric. Based on Dvorak estimates of T4.5 from TAFB and SAB,
and a SATCON estimate of 77 kt, the initial intensity is now,
somewhat surprisingly, 75 kt. Since the current intensification
trend may not be over, the official forecast calls for Florence to
strengthen just a little more during the next 6-12 hours. Even
though the hurricane will be moving over progressively warmer
waters, increasing vertical shear and dry air in the middle levels
of the atmosphere should induce some weakening in the 24-72 hour
time frame. Lower shear after 72 hours will likely allow Florence
to regain hurricane strength by the end of the forecast period.
The NHC intensity forecast is primarily adjusted to account for the
recent strengthening trend, and is closest to the Florida State
Superensemble and HCCA guidance.

Florence remains on a west-northwestward course at 300/10 kt. This
trajectory is expected to continue through 36 hours while the
hurricane remains near the southwestern edge of the subtropical
ridge. After 36 hours, Florence is expected to turn northwestward
and slow down as it enters a break in the ridge. The track models
are in good agreement and show little spread through 48 hours. On
days 3-5, the biggest outlier is the UKMET, which lies to the south
of the guidance suite. In fact, the bulk of the models, including
the deterministic GFS and ECMWF, are all now showing a more
definitive poleward motion by day 5. While the official NHC track
forecast reflects this thinking, there is still considerable spread
among the associated global model ensembles, and the longer-term
forecast should be considered low confidence.

FORECAST POSITIONS AND MAX WINDS

INIT 04/2100Z 20.3N 43.2W 75 KT 85 MPH
12H 05/0600Z 21.0N 44.8W 80 KT 90 MPH
24H 05/1800Z 22.1N 46.8W 75 KT 85 MPH
36H 06/0600Z 23.2N 48.7W 65 KT 75 MPH
48H 06/1800Z 24.3N 50.4W 60 KT 70 MPH
72H 07/1800Z 26.0N 53.0W 55 KT 65 MPH
96H 08/1800Z 27.5N 55.0W 60 KT 70 MPH
120H 09/1800Z 29.5N 56.5W 70 KT 80 MPH

$$
Forecaster Berg
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Re: ATL: FLORENCE - Advisories

#30 Postby cycloneye » Tue Sep 04, 2018 9:53 pm

Hurricane Florence Discussion Number 23
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Tue Sep 04 2018

GOES-16 imagery shows that the eye of Florence has become better
defined during the last several hours, with even some mesovortices
in the eye present on the shortwave infrared channel. Satellite
intensity estimates continue to rise, and the initial wind speed is
set to 85 kt, just below the latest TAFB estimate of 90 kt.

Florence remains on a west-northwestward course at 300/10 kt. This
general course is expected to continue through 36 or 48 hours while
the hurricane remains near the southwestern edge of the subtropical
ridge. After that time, the forecast becomes more uncertain,
depending on the presence of a narrow mid-level ridge over the
north-central Atlantic Ocean. A look at the ensemble guidance
shows a bifurcation developing by day 5, with the ECMWF favoring
a more northward turn, and the UKMET ensembles showing a stronger
ridge and a continuation of a west-northwest track. The new NHC
forecast is adjusted westward at long range, in line with the
corrected-consensus aids, but don't be surprised if this forecast
undergoes some large changes in the next few cycles, given the
split in the guidance.

This intensity forecast is also difficult. Florence certainly has
exceeded expectations during the last day or so, with the hurricane
on the verge of rapidly intensifying during the last 24 hours
despite a marginal environment. Some more strengthening is
called for in the short term to reflect the current trend.
However, the global models continue to insist that southwesterly
shear will increase over the next couple of days which, in
combination with considerable dry air aloft, should cause some
weakening. Later tomorrow, a slow weakening trend should begin and
continue through 48 hours, although not weakening as much as shown
in the past advisory. This can't be considered a high-confidence
prediction in light of what Florence has done so far. On Friday, an
upper-level low could cut off to the south of the cyclone, which
would lessen the shear near Florence, and the hurricane should be
moving over steadily increasing SSTs. Restrengthening is forecast at
long range, and it wouldn't be surprising if the new NHC prediction
turns out to be too low. It is best to be conservative, however,
since the track uncertainty is increasing by the end of the
forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 05/0300Z 20.7N 43.9W 85 KT 100 MPH
12H 05/1200Z 21.5N 45.5W 90 KT 105 MPH
24H 06/0000Z 22.6N 47.6W 80 KT 90 MPH
36H 06/1200Z 23.7N 49.4W 70 KT 80 MPH
48H 07/0000Z 24.7N 50.9W 65 KT 75 MPH
72H 08/0000Z 26.0N 53.5W 65 KT 75 MPH
96H 09/0000Z 27.3N 55.8W 70 KT 80 MPH
120H 10/0000Z 29.0N 57.5W 80 KT 90 MPH

$$
Forecaster Blake
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ATL: FLORENCE - Hurricane - Discussion

#31 Postby cycloneye » Wed Sep 05, 2018 5:01 am

Hurricane Florence Discussion Number 24
NWS National Hurricane Center Miami FL AL062018
500 AM AST Wed Sep 05 2018

Conventional satellite enhanced BD-curve infrared imagery and a
0511 UTC GMI color composite microwave pass reveal improved inner
core structure with impressive outer banding over the eastern
semicircle. Dvorak intensity estimates have again increased, and
the initial intensity is once more increased to 90 kt, which also
agrees with the latest SATCON analysis.

This intensity forecast is still a bit murky. The deterministic
models show increasing southwesterly vertical shear and a less than
favorable mid-tropospheric thermodynamic environment affecting the
tropical cyclone over the next 48 hours. This less-than-conducive
environment should induce weakening during this time frame.
Thereafter, and through the remaining forecast, most of the
models show a mid- to upper-level low developing to the south of
Florence in the base of the mid- Atlantic deep-layer trough, which
should promote a somewhat more favorable diffluent upper wind
pattern. This more conducive upper wind pattern, and increasing sea
surface temperatures, is expected to cause Florence to restrengthen.
The NHC forecast is a little bit higher than the previous one
between the 48 and 96 hr periods to agree more with the IVCN and
NOAA-HCCA consensus forecasts.

Florence is estimated to be moving northwestward, or 305/11 kt,
which appears to be a temporary trochoidal eyewall wobble. A turn
back toward the west-northwest is expected later today, and this
general motion is expected to continue through day 4 while the
hurricane is steered by the southwestern periphery of the
subtropical ridge. By the end of the forecast period, Florence is
expected to turn northwestward and slow down as it enters a break in
the ridge. The ECMWF model track forecast has shifted significantly
toward the left this evening, closer to the other global models and
their ensemble means, indicating less steering influence from the
predicted growing weakness in the subtropical ridge. Subsequently,
an adjustment to the left of of the previous advisory, beyond 48
hours, was made in order to nudge closer to the guidance suite and
the consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 05/0900Z 21.4N 44.8W 90 KT 105 MPH
12H 05/1800Z 22.2N 46.3W 90 KT 105 MPH
24H 06/0600Z 23.2N 48.2W 80 KT 90 MPH
36H 06/1800Z 24.2N 50.0W 70 KT 80 MPH
48H 07/0600Z 24.9N 51.5W 70 KT 80 MPH
72H 08/0600Z 25.6N 54.1W 75 KT 85 MPH
96H 09/0600Z 26.8N 56.3W 80 KT 90 MPH
120H 10/0600Z 28.7N 58.2W 85 KT 100 MPH

$$
Forecaster Roberts
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Re: ATL: FLORENCE - Advisories

#32 Postby cycloneye » Wed Sep 05, 2018 7:41 am

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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Re: ATL: FLORENCE - Advisories

#33 Postby cycloneye » Wed Sep 05, 2018 9:46 am

Hurricane 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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Re: ATL: FLORENCE - Advisories

#34 Postby cycloneye » Wed Sep 05, 2018 3:34 pm

Hurricane Florence Discussion Number 26
NWS National Hurricane Center Miami FL AL062018
500 PM AST Wed Sep 05 2018

Florence has continued to intensify during the day, with colder
cloud tops completely encircling a clearer eye. Both subjective and
objective Dvorak estimates have unanimously increased to T6.0/115
kt, and on this basis, the initial intensity is raised to 115 kt,
making Florence a category 4 hurricane.

Florence appears to be right along the southern edge of a zone of
stronger vertical shear and continues to defy the intensity
guidance, which has consistently been predicting weakening. That
said, the last few satellite images indicate that the eye may be
becoming slightly disrupted by the shear. Since the shear is
anticipated to increase during the next day or so, gradual weakening
is shown in the short-term official forecast, which lies along the
upper end of the guidance through 48 hours. Beyond 48 hours,
vertical shear is anticipated to weaken, which would allow Florence
to intensify and potentially regain major hurricane status. However,
Florence will need to thread the needle between areas of stronger
shear for this to happen, and there is significant uncertainty in
the intensity forecast. The new official intensity forecast is
little changed from before except to adjust upward to account for
the higher initial intensity.

The initial motion estimate remains northwestward, or 305/11 kt.
Strong upper-level ridging is forecast to strengthen north of
Florence over the next few days, forcing the hurricane to turn
toward the west-northwest through about 48 hours. Track guidance is
good agreement during this period, and the official forecast is
essentially an update to the previous one. Beyond day 2, a break
forms in the ridge, which results in a weakening of the steering
currents, a slowdown in Florence's forward speed, and a turn back
toward the northwest. The new official forecast is shifted south a
bit on days 3-5 to account for recent model trends and is closest to
the TVCN consensus.

It should be noted that there is considerable model ensemble spread
and run-to-run variability for Florence's track beyond day 5. Given
the large uncertainty at these time ranges, it is far too soon to
speculate what, if any, impacts Florence may have on the U.S. East
Coast next week. Regardless of Florence's eventual track, large
swells emanating from the hurricane will reach Bermuda beginning on
Friday, resulting in life-threatening surf and rip currents on the
island. Swells from Florence could also reach the U.S. East Coast by
early next week.

FORECAST POSITIONS AND MAX WINDS

INIT 05/2100Z 22.7N 46.6W 115 KT 130 MPH
12H 06/0600Z 23.5N 48.1W 110 KT 125 MPH
24H 06/1800Z 24.5N 49.7W 105 KT 120 MPH
36H 07/0600Z 25.2N 51.3W 100 KT 115 MPH
48H 07/1800Z 25.5N 52.9W 95 KT 110 MPH
72H 08/1800Z 26.0N 55.3W 100 KT 115 MPH
96H 09/1800Z 27.0N 57.4W 105 KT 120 MPH
120H 10/1800Z 29.0N 60.0W 105 KT 120 MPH

$$
Forecaster Berg/Rhome
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Re: ATL: FLORENCE - Advisories

#35 Postby cycloneye » Wed Sep 05, 2018 9:50 pm

Hurricane Florence Discussion Number 27
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Wed Sep 05 2018

It appears that southwesterly shear is finally affecting Florence.
The cloud pattern has become asymmetric this evening, with the
northeastern quadrant growing at the expense of the southwestern
one, along with warming cloud tops noted across the central dense
overcast. Satellite intensity estimates are a bit lower than
before, so the initial wind speed is reduced to 110 kt.

The current shear is forecast to persist by the global models during
the next day or two until an upper-level low cuts off to south of
Florence, which will likely reduce the shear. This, in combination
with much warmer waters in the path of the hurricane, should set the
stage for restrengthening. At long range, a rather large upper-level
anticyclone is forecast to form near Florence, which would provide
ample opportunity for the hurricane to regain its former strength
and grow in size. Thus, the official forecast shows slow weakening
in response to the initial shear, then levels off, with a
significant increase in strength predicted by day 5. This solution
is very close to the previous NHC advisory, but not quite as high as
the HWRF and HMON models at long range.

Florence has been moving more to the right during the past several
hours, likely due to the vortex attempting to stay vertically
aligned in the face of the southwesterly shear, but a longer-term
motion is 310 degrees at 10 kt. A mid-level ridge is forecast to
strengthen to the north and northwest of Florence, causing the
hurricane to turn west- northwestward by Friday and even westward by
the weekend. It appears that a mid-latitude trough over the
northwestern Atlantic in a few days will likely miss Florence, with
the only perceivable effects on the hurricane being a decrease in
forward speed. The net result is that the model guidance continues
to trend westward at long range, and the official forecast follows
suit, lying just north of the model consensus in deference to the
ECMWF deterministic model and ensemble mean.

It should be noted that there is still considerable model ensemble
spread for Florence's track beyond day 5. Given the large
uncertainty at these time ranges, it is far too soon to speculate
what, if any, impacts Florence may have on the U.S. East Coast next
week. Regardless of Florence's eventual track, large swells
emanating from the hurricane will reach Bermuda beginning on Friday,
resulting in life-threatening surf and rip currents on the island.
Swells from Florence could also reach the U.S. East Coast by early
next week.


FORECAST POSITIONS AND MAX WINDS

INIT 06/0300Z 23.4N 47.2W 110 KT 125 MPH
12H 06/1200Z 24.2N 48.4W 105 KT 120 MPH
24H 07/0000Z 25.0N 49.9W 100 KT 115 MPH
36H 07/1200Z 25.5N 51.6W 95 KT 110 MPH
48H 08/0000Z 25.7N 53.2W 95 KT 110 MPH
72H 09/0000Z 26.1N 55.7W 100 KT 115 MPH
96H 10/0000Z 27.2N 58.1W 105 KT 120 MPH
120H 11/0000Z 29.0N 62.0W 115 KT 130 MPH

$$
Forecaster Blake
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Re: ATL: FLORENCE - Advisories

#36 Postby cycloneye » Thu Sep 06, 2018 4:28 am

Hurricane Florence Discussion Number 28
NWS National Hurricane Center Miami FL AL062018
500 AM AST Thu Sep 06 2018

Southwesterly shear continues to affect Florence. Since the last
advisory, the cloud pattern has become more asymmetric, and cloud
tops surrounding the ragged eye have warmed. AMSR imagery around
0430 UTC indicated that the hurricane's eye is tilted slightly
southwest to northeast with height, but the low- to mid-level
inner-core was mostly intact. Based on an average of Final-T and
CI numbers from TAFB and SAB, the initial intensity has been lowered
to 100 kt, and objective estimates are even lower.

Given the wind shear and current appearance of Florence, additional
weakening in the short-term seems likely, and all of the intensity
guidance agrees. From 24-72 h, the spread increases with the
statistical models generally showing continued gradual weakening for
another day or two, while the dynamical models show little change or
slight restrengthening. By day 5, all of the guidance calls for
Florence to restrengthen. The guidance envelope and consensus is
lower with this model cycle, but the NHC intensity forecast has only
been adjusted slightly lower, mainly in the first 72 h of the
forecast. The official forecast is now a little above the IVCN
intensity consensus and HCCA at most forecast hours, generally
favoring the stronger solution of the dynamical models.

Florence has continued to track northwestward, and the initial
motion is 315/10 kt. The cyclone is still forecast to gradually
turn westward over the next 48 h, in response to a building
mid-level ridge to its north. Beyond that time, a mid-latitude
trough over the northwestern Atlantic could create enough of a
weakness in the ridge to steer the hurricane farther north, closer
to Bermuda, as shown by the latest GFS. However, the ECMWF and
UKMET suggest that the ridge will not be significantly affected, and
Florence will move more westward. The ensembles from the GFS and
ECMWF do not clearly favor one solution over another, and in fact
many members track Florence somewhere in-between. While little
change was made to the previous forecast and the new official track
forecast remains close to the various consensus aids, the model
spread has increased and confidence in the forecast is low.

There is still considerable model ensemble spread for Florence's
track beyond day 5. Given the large uncertainty at these time
ranges, it is far too soon to speculate what, if any, impacts
Florence may have on the U.S. East Coast next week. Regardless of
Florence's eventual track, large swells emanating from the hurricane
will reach Bermuda beginning on Friday and portions of the U.S. East
Coast this weekend, resulting in life-threatening surf and rip
currents.

FORECAST POSITIONS AND MAX WINDS

INIT 06/0900Z 24.1N 47.9W 100 KT 115 MPH
12H 06/1800Z 24.8N 49.1W 90 KT 105 MPH
24H 07/0600Z 25.4N 50.8W 90 KT 105 MPH
36H 07/1800Z 25.6N 52.2W 90 KT 105 MPH
48H 08/0600Z 25.6N 53.6W 90 KT 105 MPH
72H 09/0600Z 26.1N 56.1W 95 KT 110 MPH
96H 10/0600Z 27.2N 59.0W 105 KT 120 MPH
120H 11/0600Z 29.0N 63.5W 110 KT 125 MPH

$$
Forecaster Zelinsky
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Re: ATL: FLORENCE - Advisories

#37 Postby cycloneye » Thu Sep 06, 2018 9:41 am

Hurricane Florence Discussion Number 29
NWS National Hurricane Center Miami FL AL062018
1100 AM AST Thu Sep 06 2018

Vertical shear has increased since yesterday, which has caused a
degradation of Florence's structure and a decrease in its maximum
winds. The cloud-filled eye has been eroded over the past hour or
so, and the deep convection is no longer symmetric, with the
low-level circulation peeking out from under the higher clouds.
Dvorak CI numbers from TAFB and SAB have fallen to T5.0-5.5 (90-100
kt), while the objective numbers from UW-CIMSS support 70-90 kt.
The initial intensity is set at 90 kt, near the middle of this wide
range of estimates.

The intensity forecast has been somewhat of a self-defeating
prophecy due to the nuances of the environmental shear. Even though
Florence was able to rapidly intensify yesterday in an area just
south of a zone of strong shear, the hurricane's stronger-than-
expected intensity caused it to move more poleward, into that
stronger shear. Right now, shear analyses range anywhere from
25-30 kt, and the latest available guidance suggests that this
level of shear should continue for another 12-24 hours. As a
result, continued weakening is forecast over the next day or so.
After 36 hours, Florence is likely to encounter an upper-level
environment that is more conducive for reintensification. The NHC
forecast is adjusted downward toward the newest consensus aids,
especially during the first 48 hours, but it still shows Florence
reaching major hurricane strength again by days 4 and 5.

Florence's forward motion has slowed just a little to 9 kt toward
the northwest (315 degrees). A mid-level ridge is building to the
north, which is likely to cause the hurricane to turn westward by
36 hours, with that motion continuing through about day 3. After
that time, there is still considerable uncertainty in the evolution
of the steering pattern over the western Atlantic, especially on day
4. On one hand, the GFS and HWRF dig a strong shortwave trough over
Atlantic Canada by Monday, creating a break in the ridge which would
allow Florence to turn northwestward. On the other hand, the ECMWF
and UKMET both have weaker troughs and maintain stronger ridging
over the northwestern Atlantic, allowing Florence to maintain a
westward or west-northwestward course. All the models show a
mid-level high over the western Atlantic by Tuesday. Due to typical
biases among these models in the part of the Atlantic, we prefer to
be between the GFS and ECMWF solutions at this time, which places
the official NHC track forecast close to the TVCN multi-model
consensus and just north of HCCA.

There is still considerable model ensemble spread for Florence's
track beyond day 5. Given the large uncertainty at these time
ranges, it is far too soon to speculate what, if any, impacts
Florence may have on the U.S. East Coast next week. Regardless of
Florence's eventual track, large swells emanating from the hurricane
will reach Bermuda beginning on Friday and portions of the U.S. East
Coast this weekend, resulting in life-threatening surf and rip
currents.

FORECAST POSITIONS AND MAX WINDS

INIT 06/1500Z 24.6N 48.6W 90 KT 105 MPH
12H 07/0000Z 25.2N 49.8W 80 KT 90 MPH
24H 07/1200Z 25.6N 51.3W 75 KT 85 MPH
36H 08/0000Z 25.6N 52.6W 75 KT 85 MPH
48H 08/1200Z 25.7N 54.0W 80 KT 90 MPH
72H 09/1200Z 26.3N 56.4W 90 KT 105 MPH
96H 10/1200Z 28.0N 59.5W 100 KT 115 MPH
120H 11/1200Z 29.5N 65.0W 105 KT 120 MPH

$$
Forecaster Berg
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Re: ATL: FLORENCE - Advisories

#38 Postby cycloneye » Thu Sep 06, 2018 7:34 pm

Hurricane Florence Discussion Number 30
NWS National Hurricane Center Miami FL AL062018
500 PM AST Thu Sep 06 2018

Vertical shear has taken its toll on Florence today as evidenced by
a continued degradation of the overall cloud pattern. The
circulation appears tilted, with the low-level center partially
exposed to the southwest of the deep convection. Subjective and
objective Dvorak Current Intensity (CI) numbers have fallen, and a
blend of the various estimates supports an initial intensity of 70
kt.

The intensity forecast is relatively straightforward in the
short-term as shear is expected to remain strong, which should
continue Florence's weakening trend, potentially taking the system
below hurricane strength. By 24 hours, vertical shear is forecast
to decrease, and the SSTs gradually warm along the forecast track.
Assuming the overall circulation remains intact, Florence shouldn't
have any problems restrengthening beginning in a day or so. In
fact, guidance suggests that Florence could once again become a
major hurricane in 4 or 5 days. The new NHC intensity forecast is
essentially an update of the previous one, and is only adjusted to
account for recent trends. Largely, the official forecast is close
to the various consensus aids.

Owing to the degraded structure and tilted nature of the system,
Florence has wobbled a bit to the west, but the longer-term motion
estimate is 305/09. Low- to mid-level ridging should cause
Florence to turn toward the west-northwest and west between 12-48
hours while the cyclone recovers from the strong shear. Thereafter,
Florence is anticipated to become a deep cyclone again, but an even
stronger ridge should maintain the west-northwestward motion, at a
faster speed, through day 5. The ridge is forecast to be
sufficiently strong such that some track models show a motion just
south of due west during the next 12-36 hours. Beyond day 3, the
track forecast becomes increasingly uncertain due to differing
evolutions of the steering pattern over the western Atlantic. While
all of the global models show a progressive trough eroding the
ridge, they differ in the strength of the trough and the ridge to
the north of Florida. These differences result in a great deal of
bifurcation in the track guidance, especially among global model
ensemble members, at the end of the forecast period. In such
situations, prudence suggests a reliance on continuity, and the the
new official NHC track forecast is shifted only slightly south
towards the TVCN multi-model consensus and HCCA. 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.

Key Messages:

1. Regardless of Florence's eventual track, large swells will begin
to affect Bermuda on Friday 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.

FORECAST POSITIONS AND MAX WINDS

INIT 06/2100Z 25.0N 49.6W 70 KT 80 MPH
12H 07/0600Z 25.4N 50.7W 60 KT 70 MPH
24H 07/1800Z 25.5N 52.1W 65 KT 75 MPH
36H 08/0600Z 25.5N 53.4W 70 KT 80 MPH
48H 08/1800Z 25.6N 54.6W 75 KT 85 MPH
72H 09/1800Z 26.4N 57.1W 90 KT 105 MPH
96H 10/1800Z 28.0N 61.0W 100 KT 115 MPH
120H 11/1800Z 30.0N 67.0W 105 KT 120 MPH

$$
Forecaster Berg/Rhome
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Re: ATL: FLORENCE - Advisories

#39 Postby cycloneye » Thu Sep 06, 2018 9:44 pm

BULLETIN
Tropical Storm Florence Advisory Number 31
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Thu Sep 06 2018

...FLORENCE EXPECTED TO REINTENSIFY ON FRIDAY...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...25.1N 49.8W
ABOUT 975 MI...1570 KM ENE OF THE NORTHERN LEEWARD ISLANDS
ABOUT 1035 MI...1665 KM ESE OF BERMUDA
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 7 MPH...11 KM/H
MINIMUM CENTRAL PRESSURE...993 MB...29.33 INCHES



Tropical Storm Florence Discussion Number 31
NWS National Hurricane Center Miami FL AL062018
1100 PM AST Thu Sep 06 2018

Deep convection near the center of Florence has continued to
decrease during the past several hours, and the overall cloud
pattern remains elongated from southwest to northeast. The latest
Dvorak estimates and a recent scatterometer pass suggest that
Florence is no longer a hurricane, and the initial wind speed is
set to 60 kt.

Some further weakening is anticipated since the shear isn't forecast
to change much in the short term. However, all of the global models
show a significant reduction of shear during the next several days,
especially later this weekend. In combination with waters warming
to near 29C, these conditions should promote strengthening into a
hurricane again in a day or two and a major hurricane by early next
week. The intensity guidance is higher than the last cycle at long
range, which is hard to argue with considering the large upper-level
anticyclone forecast in the vicinity of Florence. The NHC intensity
forecast follows the trend of the previous prediction, a bit
elevated from the previous forecast at days 4 and 5, although still
below the intensity guidance.

A recent scatterometer pass indicates that Florence has slowed down
and turned left, estimated at 290/6. A narrow ridge over the
subtropical Atlantic Ocean should continue to turn the storm
westward overnight, albeit traveling at a relatively slow pace due
to the strength of the ridge. This ridge is forecast is strengthen
at long range, steering Florence faster to the west-northwest over
the western Atlantic Ocean. Except for the UKMET, most of the
historically reliable guidance is in reasonable agreement on this
scenario, which is a bit surprising given the recent trials and
tribulations from the guidance suite. The models continue to shift
westward at long range, however, owing to differences on the
strength and position of that ridge, and the official NHC track
forecast is moved in that direction.


Key Messages:

1. Regardless of Florence's eventual track, large swells will begin
to affect Bermuda on Friday 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.


FORECAST POSITIONS AND MAX WINDS

INIT 07/0300Z 25.1N 49.8W 60 KT 70 MPH
12H 07/1200Z 25.2N 50.8W 55 KT 65 MPH
24H 08/0000Z 25.2N 52.2W 60 KT 70 MPH
36H 08/1200Z 25.2N 53.6W 65 KT 75 MPH
48H 09/0000Z 25.3N 54.7W 75 KT 85 MPH
72H 10/0000Z 26.1N 57.3W 90 KT 105 MPH
96H 11/0000Z 27.6N 62.2W 105 KT 120 MPH
120H 12/0000Z 30.0N 68.5W 110 KT 125 MPH

$$
Forecaster Blake
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Re: ATL: FLORENCE - Advisories

#40 Postby cycloneye » Fri Sep 07, 2018 5:07 am

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.

FORECAST POSITIONS AND MAX WINDS

INIT 07/0900Z 25.1N 50.7W 55 KT 65 MPH
12H 07/1800Z 25.1N 51.8W 55 KT 65 MPH
24H 08/0600Z 25.0N 53.2W 55 KT 65 MPH
36H 08/1800Z 25.0N 54.3W 60 KT 70 MPH
48H 09/0600Z 25.1N 55.4W 70 KT 80 MPH
72H 10/0600Z 26.2N 58.3W 95 KT 110 MPH
96H 11/0600Z 27.5N 63.5W 110 KT 125 MPH
120H 12/0600Z 30.0N 70.0W 110 KT 125 MPH

$$
Forecaster Zelinsky
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