Windspeed

Didn't Harvey intesy to a category 4 just before landfall? 

 

Harvey had exceptional upper atmospheric environmental conditions on approach, a tight vortex and 30-31°C up to the shoreline. Florence is a much larger hurricane. It's not impossible that Florence could make landfall as a Cat 4, it's just not as likely based on slow movement in a less favorable environment.

 

 

Agree on the Cat 3 intensity. However, the windfield is expanding. This poses an increase in surge potential for a slow-moving landfall or stall near landfall. Greater fetch. Additionally, even with expansion of windfield, favorable environmental conditions can still result in intensification of the core vortex. We still have a long ways to go. It wouldn't be unrealistic for reintensification back to a Cat 4 and then additional weakening trend near landfall.

 

 

 

 

 

What exactly is a moat in a hurricane?

 

We use "moat" to describe the area of subsidence that occurs due to an outer rain band intensifying to the point of forming an outer concentric ring of convection or "outer eyewall". This isn't quite there yet based on earlier microwave, however, clearly there is a strong outer band right now causing that subsidence and it could lead to concentric walls if it continues to organize.

Strong convection in the southern band. Even looks like it is creating a moat of subsidence outside SW portion of the eyewall. Even though Florence has a decent-sized eye, don't be surprised at another ERC cycle and an even larger eye. The current eye also does look to be contracting a bit.

 

 

 

Oh! Didn't realize this was them, my bad. Yes, I really enjoy "Stewart" discussions. 

 

Nice save there!

 

Do you have a link to something recent to read?

https://www.nhc.noaa.gov/text/refresh/MIATCDAT1+shtml/112056.shtml

Stacy Stewart is the master of meteorological discussion of TCs and synoptic reasoning. That is all.

545 
WTNT41 KNHC 112056
TCDAT1

Hurricane Florence Discussion Number  50
NWS National Hurricane Center Miami FL       AL062018
500 PM AST Tue Sep 11 2018

Microwave satellite data indicate that Florence completed a full
eyewall replacement cycle (ERC) a few hours ago, and recent visible
and infrared imagery suggests that the eye has contracted slightly.
Outflow continues to expand in all quadrants, and the outflow jets
to the northwest and east have become better defined. Satellite
intensity estimates from TAFB, SAB, and UW-CIMSS ADT are all
T6.0/115 kt, and recent NHC objective intensity estimates are
T6.2/120 kt. Given that the eye has mostly cleared out and has also
warmed to near 19 deg C, the initial intensity has been bumped
upward to 120 kt, which could be conservative. All of the wind radii
had to be expanded/increased based on a blend of the earlier
reconnaissance data and a 1430 UTC ASCAT scatterometer pass.

The initial motion estimate is now 300/15 kt. There remains no
significant to the previous track forecast or reasoning. Overall,
the global and regional models have done a good job capturing the
evolving synoptic- scale flow pattern across CONUS, with an
amplifying trough moving onshore the the northwestern U.S. coast,
which is inducing downstream ridging across the northeastern U.S.
and the northwestern Atlantic Ocean. Water vapor imagery indicates
that the blocking high pressure northwest of Bermuda is continuing
to build and shift slowly eastward. The 12Z GFS model made a
significant shift to the west, the UKMET made a shift to the east,
and the ECMWF track has remained basically unchanged through 72
hours. As a result the consensus models have made only minor track
shifts to the west. What is noticeable is that all of the global and
regional models are indicating that the steering currents will
collapse by 72 h when Florence is approaching the southeast U.S.
coast. The weak steering currents are expected to continue through
the weekend, which makes the forecast track on days 3-5 quite
uncertain. The latest NHC forecast track is very similar to the
previous two advisory tracks, and lies the middle of the guidance
envelope between the consensus models TVCA to the north and the HCCA
and FSSE models to the south.

During the next 24 hours or so, Florence is expected to remain in a
very favorable environment consisting of low shear near 5 kt, an
expanding upper-level outflow pattern, and above-average SSTs of
29.0-29.5 deg C, which should result in additional strengthening.
By 48 h, the decreasing forward speed along with the large
inner-core wind field should induce some upwelling and gradual
weakening. Although the GFS- and ECMWF-based SHIPS intensity models
are indicating an increase in the southwesterly shear to near 20 kt,
this could be due to the SHIPS model capturing Florence's own
strong outflow from the GFS and ECMWF model fields. Despite the
weakening shown at 72 hours, Florence is still expected to remain a
dangerous hurricane through landfall. After Florence moves inland,
the slow forward speed of less than 5 kt should cause a rapid spin
down and weakening of the hurricane's circulation. The new NHC
intensity forecast is a little above the highest guidance based on
the aforementioned very favorable synoptic outflow pattern, and to
maintain continuity with the previous forecast.

Key Messages:

1. A life-threatening storm surge is now highly likely along
portions of the coastlines of South Carolina and North Carolina, and
a Storm Surge Warning is in effect for a portion of this area. All
interests from South Carolina into the mid-Atlantic region should
ensure they have their hurricane plan in place and follow any advice
given by local officials.

2. Life-threatening, catastrophic flash flooding and significant
river flooding is likely over portions of the Carolinas and
Mid-Atlantic states from late this week into early next week, as
Florence is expected to slow down as it approaches the coast and
moves inland.

3. Damaging hurricane-force winds are likely along portions of the
coasts of South Carolina and North Carolina, and a Hurricane Warning
has been issued for a part of this area.  Damaging winds could also
spread well inland into portions of the Carolinas and Virginia.

4. Large swells affecting Bermuda and portions of the U.S. East
Coast will continue this week, resulting in life-threatening surf
and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  11/2100Z 27.5N  67.1W  120 KT 140 MPH
 12H  12/0600Z 28.7N  69.3W  130 KT 150 MPH
 24H  12/1800Z 30.4N  72.1W  135 KT 155 MPH
 36H  13/0600Z 32.1N  74.5W  130 KT 150 MPH
 48H  13/1800Z 33.4N  76.2W  120 KT 140 MPH
 72H  14/1800Z 34.5N  77.7W  100 KT 115 MPH...NEAR THE COAST
 96H  15/1800Z 35.0N  78.8W   40 KT  45 MPH...INLAND
120H  16/1800Z 35.7N  81.7W   25 KT  30 MPH...INLAND

$$
Forecaster Stewart

 

sup...i'm unbanned.  glad the mods saw the light and went SEP and it was fun watching you all trash njwx85, mr "this is definitely hitting as a cat 4" anyone else think icyclone should have chased mangkut? it's looking like irma for sure

Exposure. Exposure. Exposure. Western media and the threat is great in a highly publicized event. The possibility of a stall on the coastline could also make for a long-duration event. Something Josh has not had a lot of dealings with versus short intense landfalls. Also he already explained his reasoning in potential difficulties in chasing and penetrating Mangkhut in the Luzon Strait as well. I think he made a good call.

Images Me thinks that system in the gulf gonna have something to do with where Flo goes in the end.... Def starting to blow up down there.

This really needs its own thread vs lagging down the main thread. 

Edit: Thanks for fixing and embedding one main animated url image versus 20+.

 

 

 

 

 

 

 

 

 

 

 

New 12z ECMWF totals:

This is a cruel run for Wilmington. SW drift would keep onshore flow surging Cape Fear for several days.

Doesn't appear to make landfall this run, but drift just offshore 

Yes, through 96 it stalls and fails to make landfall. Drifting SW.

ECMWF is a slow agonizing landfall between Wilmington and Jacksonville, NC., and a long-duration hurricane force wind event over shoreline. Florence would be weakening, but slowly until core got inland. Even if you don't get sustained major hurricane force for very long, 24-36 hrs straight of hurricane force winds is going to be devastating.

 

Edit: Fails to make landfall through 96. Just stalls near shore and then begins to drift SW.

 

 

Maybe I'm forgetting but I don't recall seeing a storm with that satellite presentation before.  What's the deal with the fingers of cooler cloud tops oriented straight out from the center?

 

It's due to strong divergence aloft. You have strong upper level airflow jets away from the convection that stretches the high cirrus clouds. It creates finger-like linear striations / furrows in the cloud canopy's appearance. Essentially, the CDO is being stretched and it's also a sign of strong outflow channeling establishing.

 

Now that the GFS has produced a run that looks more realistic, let's analyze the nice ventilation on approach. Look at that Hugo-esque outflow channel to the SW. This is the same one the ECMWF had been showing around the 400-300 mb ULL over Florida. Florence will be near the edge of a southerly shear axis. I'm not yet sure if that will merely be adjacent to the southern mid-level circulation or over it. If it is over, then certainly a faster stall would induce weakening; however, if WNW motion doesn't stall until after landfall, Florence may not weaken much for it, and in fact, may be enhanced by upper-level easterly flow away from the core. This would be a timing issue between 54 and 72 hrs depending on slowdown of steering flow.

12z ECMWF is probably going to be close enough now to start nailing down that stall. It had it just inland on the 0z.

273 
WTNT44 KNHC 101436
TCDAT4

Hurricane Isaac Discussion Number  12
NWS National Hurricane Center Miami FL       AL092018
1100 AM AST Mon Sep 10 2018

Isaac's cloud pattern is currently a bit ragged-looking, with an
irregular CDO and limited convective banding.  Dvorak intensity
estimates from both TAFB and SAB are 65 kt, and that value will be
used for the advisory.  There is significant uncertainty in the
intensity forecast for this system.  Vertical wind shear over the
hurricane is forecast to be weak to moderate during the next day or
so, which should allow Isaac to strengthen somewhat.  By 48 hours,
however, the global models depict significantly stronger
northwesterly shear, associated with an upper-level trough over the
central Atlantic, affecting the tropical cyclone.  Most of the
guidance does not show Isaac strengthening over the Caribbean.  The
HWRF model is an outlier, strengthening Isaac into a major hurricane
later in the period, and it is the main contributor to high
consensus forecasts at days 3-5.  The NHC intensity forecast is
above the model consensus through 72 hours and below it by the end
of the period.

Isaac continues to move westward, or 275/12 kt.  A subtropical
ridge should be maintained to the north of the tropical cyclone for
the next several days, so a continued westward track seems likely.
The U. K. Met. Office model is an outlier and shows Isaac turning
northwestward and northward to the northeast of the Leeward Islands.
The official track forecast, like the previous one, follows the
other reliable global models and is also close to the HFIP corrected
consensus guidance.

Key Messages:

1. Isaac is a small hurricane and uncertainty in the forecast is
greater than normal.  Although Isaac is forecast to begin weakening
when it approaches the Lesser Antilles, it is still expected to be
at or near hurricane intensity when it reaches the islands.

2. Interests in the Lesser Antilles should continue to monitor Isaac
during the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT  10/1500Z 14.7N  43.9W   65 KT  75 MPH
 12H  11/0000Z 14.9N  45.9W   70 KT  80 MPH
 24H  11/1200Z 15.0N  48.7W   75 KT  85 MPH
 36H  12/0000Z 15.0N  51.4W   75 KT  85 MPH
 48H  12/1200Z 15.1N  54.0W   75 KT  85 MPH
 72H  13/1200Z 15.4N  59.4W   70 KT  80 MPH
 96H  14/1200Z 15.5N  64.5W   60 KT  70 MPH
120H  15/1200Z 15.7N  70.0W   50 KT  60 MPH

$$
Forecaster Pasch

 

Helene expected to become a major hurricane before lifting north into east-central Atlantic and weakening.

274 
WTNT43 KNHC 101436
TCDAT3

Hurricane Helene Discussion Number  13
NWS National Hurricane Center Miami FL       AL082018
1100 AM AST Mon Sep 10 2018

Helene's cloud pattern has become much better organized during the
past few hours, with a clear 20 n mi wide eye seen in Meteosat
infrared imagery, and a clear eye noted in a 1135 UTC AMSU overpass.
A Dvorak classifications from TAFB and SAB were both T5.0/90 knots
at 1200 UTC, and that is the initial intensity for this advisory.
Helene will remain in an environment that should support some
additional strengthening for the next 12 hours or so, with very low
shear and SSTs of 27C or above. After that time, the SSTs cool
quickly and the shear increases dramatically by 36 hours, which
should induce steady weakening. Late in the period, the shear
continues, and while SSTs increase the atmosphere dries out, and the
intensity is held steady at day 5. The new NHC intensity forecast is
above most of the guidance through 24 hours to account for the
recent intensification of the storm, but then is close to or
slightly above HCCA and IVCN.

The initial motion estimate is 285/14. The subtropical ridge north
of Helene will gradually weaken as an upper-level trough digs
southward around 40W. This pattern will cause Helene to slow down
and gradually recurve during the forecast period, with a faster
northward motion expected at days 4 and 5 as Helene interacts with
the aforementioned upper-level trough. While there is significant
variability between the various global models in the exact
evolution of the upper-level pattern, the track model guidance is
in generally good agreement on this evolution, although the UKMET,
its ensemble mean and the GEFS mean are notable outliers to the
right. The new NHC track was not changed much from the previous one
and lies near the middle of the guidance envelope and is close to
HCCA.

FORECAST POSITIONS AND MAX WINDS

INIT  10/1500Z 14.6N  30.0W   90 KT 105 MPH
 12H  11/0000Z 15.2N  32.0W  100 KT 115 MPH
 24H  11/1200Z 15.9N  34.3W  100 KT 115 MPH
 36H  12/0000Z 16.8N  36.1W   90 KT 105 MPH
 48H  12/1200Z 18.0N  37.7W   75 KT  85 MPH
 72H  13/1200Z 21.5N  39.5W   60 KT  70 MPH
 96H  14/1200Z 27.0N  40.5W   50 KT  60 MPH
120H  15/1200Z 32.5N  40.5W   50 KT  60 MPH

$$
Forecaster Brennan

 

[mention=845]Windspeed[/mention], what do you think?  Is this making a landfall in the SE, and if so, do we feel the impacts in this area?  We really want no part of that monster.

Apologies, as I did not notice this until now. I think Florence does make landfall. It's current location and the WAR at 500mb is building into the Mid-Atlantic well enough to get the TC into the Carolinas. The big question for us is how ridging over the Ohio Valley to New England evolves versus surface highs / upper trough over Central and Upper Plains. If we're looking at a more amplified pattern / advancing trough, western edge of WAR should erode. Florence should run into a brick wall and the destructive precip shield should remain over Piedmont and coastal plain until it gets kicked out. However, if it is less amplified and Florence gets tucked under a negligible steering flow, stronger 500mb heights from Ohio to NE could leave a stall further NW or WNW over the Blue Ridge. That could potentially bring the destructive precip shield over W NC/VA highlands, perhaps even NE TN, SWVA. So closely watching how this plays out. I don't want to go all hyperbole at the risk yet because a lot can still change in 96-144 hrs range with respect to our neck of the woods.

Excellent piece of ground breaking information in from Phillip Klotzbach regarding Florence this evening. I just wanna say that we are so blessed to have people around that can share this kind of revolutionary insight with us.

(posted as an image as tweet wouldn't embed properly.)

To be fair, he's responding to person's question on Twitter. I'm surprised he didn't begin by explaining what a surface low is...

251 
WTNT44 KNHC 090242
TCDAT4

Tropical Storm Isaac Discussion Number   6
NWS National Hurricane Center Miami FL       AL092018
1100 PM AST Sat Sep 08 2018

Isaac is strengthening this evening.  Satellite images indicate that
the deep convection has been increasing in intensity and coverage
with better defined banding features.  The center is not located in
the center of the convection, however, due to some easterly shear.
An ASCAT pass around 00Z showed maximum winds in the 40-45 kt
range.  These data are also in line with the latest Dvorak
classifications of 3.0/45 kt from TAFB and SAB.  Based on these
estimates, the initial intensity is raised to 45 kt.

Isaac will likely continue to strengthen during the next few days as
the storm remains over warm waters and moves into an environment of
decreasing wind shear.  Beyond a few days, the SHIPS model shows a
notable increase in shear, in part due to the outflow from Florence,
which should end the strengthening trend and cause some weakening.
With the exception of the HMON and COAMPS-TC models, the remainder
of the intensity guidance is higher this cycle.  The NHC intensity
forecast is raised from the previous one, but it is a little lower
than the HCCA and IVCN guidance.

The storm is moving due westward at 7 kt.  The track forecast seems
fairly straightforward.  A strengthening subtropical ridge to the
north of the system should cause Isaac to move westward at an
increasing forward speed during the next several days.  This
scenario is supported by the usually more reliable GFS and ECMWF
models, and the NHC track forecast is near a blend of those aids.
Based on the current forecast, Isaac will be near the Lesser
Antilles in 4 to 5 days and interests there should monitor the
progress of this system.

FORECAST POSITIONS AND MAX WINDS

INIT  09/0300Z 14.4N  37.5W   45 KT  50 MPH
 12H  09/1200Z 14.4N  38.7W   50 KT  60 MPH
 24H  10/0000Z 14.5N  40.9W   60 KT  70 MPH
 36H  10/1200Z 14.5N  43.5W   70 KT  80 MPH
 48H  11/0000Z 14.5N  46.1W   75 KT  85 MPH
 72H  12/0000Z 14.5N  51.5W   85 KT 100 MPH
 96H  13/0000Z 14.6N  57.0W   80 KT  90 MPH
120H  14/0000Z 15.0N  62.9W   75 KT  85 MPH

$$
Forecaster Cangialosi

 

Yeah I am a little puzzled at the HWRF's intensity, however, it is possible the shear axis from the Florence's outflow channel will stay north of Isaac due to a cutoff low in the central Atl., east of Bermuda. Also, a TUTT may develop over the Greater Antilles, which, if Isaac is positioned just right, there could be a sufficient upper ridge east of the Leewards to support major hurricane intensity. Granted, Isaac may encounter an unfavorable environment as it traverses deeper into the Caribbean. Unfortunately, it may have already impacted hard hit areas from last year before it reaches a more unfavorable environment.

510 
WTNT44 KNHC 082048
TCDAT4

Tropical Storm Isaac Discussion Number   5
NWS National Hurricane Center Miami FL       AL092018
500 PM AST Sat Sep 08 2018

The structure of the cyclone, while still a shear pattern, is
improving, with the low-level center now near the convective
overcast and improved outflow in the eastern semicircle.  Satellite
intensity estimates have increased to the 30-45 kt range, with the
CIMSS satellite consensus technique now suggesting winds near 35
kt.  Based on these estimates, the initial intensity is increased to
35 kt and the depression is upgraded to Tropical Storm Isaac.

Isaac is now moving slowly westward, with the initial motion 275/6.
The subtropical ridge to the north of Isaac is forecast to steer the
system westward with an increasing forward speed for at least the
next 2-3 days.  After that time, there is some uncertainty in the
track forecast due to the formation of a mid- to upper-level trough
over the central Atlantic, with some of the track guidance showing a
decrease in forward speed and a more northerly motion near the end
of the forecast period.  The GFS and ECMWF models show a continued
westerly motion through that time, and the official forecast follows
that scenario, although with a slower forward speed than in the
previous forecast.  The new forecast is again similar to the
earlier forecast and lies near the various consensus models.

Conditions appear favorable for gradual strengthening during the
next 72 h as Isaac moves westward across the warm waters of the
tropical Atlantic.  In best agreement with the SHIPS model for the
next three days, the new intensity forecast is raised from the
previous forecast during this time.  From 72-120 h, the system is
expected to encounter westerly wind shear, which is expected to
cause some weakening.


FORECAST POSITIONS AND MAX WINDS

INIT  08/2100Z 14.5N  36.6W   35 KT  40 MPH
 12H  09/0600Z 14.6N  37.7W   40 KT  45 MPH
 24H  09/1800Z 14.7N  39.5W   50 KT  60 MPH
 36H  10/0600Z 14.7N  42.0W   60 KT  70 MPH
 48H  10/1800Z 14.7N  44.6W   65 KT  75 MPH
 72H  11/1800Z 14.5N  50.0W   75 KT  85 MPH
 96H  12/1800Z 14.5N  55.5W   75 KT  85 MPH
120H  13/1800Z 15.0N  61.0W   70 KT  80 MPH

$$
Forecaster Beven

 

12 minutes ago, WxWatcher007 said:

Looking like this could be Isaac at 5pm.

 

Little doubt. One look at the visible and even though the TC is still encounter mid-level easterly shear, that i abating. Convection canopy and MLC looks slightly more aligned. If you focus on low-level cumulus cloud flow on the south side of circulation, it is screaming east. This has got to be of TS intensity.

Edit: Oops. Board is lagging and messed up initial post.

 

720 
WTNT44 KNHC 080255
TCDAT4

Tropical Depression Nine Discussion Number   2
NWS National Hurricane Center Miami FL       AL092018
1100 PM AST Fri Sep 07 2018

The depression continues to be impeded by moderate easterly shear
with the center of circulation decoupled to the east of a deep
convective banding feature.  The initial intensity is held at 30 kt
based on subjective intensity estimates from TAFB and SAB.

The dynamical-statistical intensity guidance, as well as the
large-scale models, indicate that the shear should diminish to less
than 10 kt within the next 24 hours.  A more favorable upper-wind
pattern along with warm oceanic temperatures is expected to promote
steady strengthening commencing after that time.  The intensity
forecast is based on a blend of the IVCN and the HCCA consensus
models and remains below the stronger HWRF at days 4 and 5.

The depression has been meandering during the past several
hours, as a result of weak low- to mid-level steering currents
created by a deep-layer trough digging southward over the eastern
Atlantic.  In 12 to 24 hours, a westward motion with a gradual
increase in forward speed is forecast thereafter as the trough lifts
northeast, and the subtropical ridge re-establishes to the north of
the cyclone.  The NHC track forecast lies closest to the HCCA and
TVCN guidance and takes the system toward the Lesser Antilles by the
end of the forecast period.


FORECAST POSITIONS AND MAX WINDS

INIT  08/0300Z 13.9N  34.9W   30 KT  35 MPH
 12H  08/1200Z 14.1N  35.6W   35 KT  40 MPH
 24H  09/0000Z 14.2N  36.7W   35 KT  40 MPH
 36H  09/1200Z 14.3N  38.4W   45 KT  50 MPH
 48H  10/0000Z 14.4N  40.4W   55 KT  65 MPH
 72H  11/0000Z 14.4N  45.2W   75 KT  85 MPH
 96H  12/0000Z 14.4N  50.2W   80 KT  90 MPH
120H  13/0000Z 14.9N  56.2W   85 KT 100 MPH

$$
Forecaster Roberts