Major Hurricane Florence

[WxWatcher007]

Looks like we're close enough to a named system that advisories are starting in about a half hour. Almost certainly a fish storm, but looking likely on the guidance to become the strongest system of the year so far. 

NHC will initiate advisories at 11 am EDT on Potential Tropical Cyclone Six, located east-southeast of the Cabo Verde Islands.

 

Edited to add. This was the first cone lol

[yoda]

BULLETIN
Potential Tropical Cyclone Six Advisory Number   1
NWS National Hurricane Center Miami FL       AL062018
1100 AM AST Thu Aug 30 2018

...TROPICAL STORM CONDITIONS EXPECTED OVER THE SOUTHERN CABO VERDE
ISLANDS ON FRIDAY...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...12.9N 18.4W
ABOUT 425 MI...680 KM ESE OF THE SOUTHERNMOST CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...30 MPH...45 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:

The government of the Cabo Verde Islands has issued a Tropical
Storm Warning for the southern islands of Santiago, Fogo and
Brava.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Warning is in effect for...
* Santiago
* Fogo
* Brava

A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area within 36 hours.

For storm information specific to your area, please monitor products
issued by your national meteorological service.


DISCUSSION AND OUTLOOK
----------------------
At 1100 AM AST (1500 UTC), the disturbance was centered near
latitude 12.9 North, longitude 18.4 West. The system is moving
toward the west near 12 mph (19 km/h), and this general motion
with a gradual turn toward the west-northwest is expected to
continue during the next few days. On the forecast track, the
disturbance is expected to move near or over the southern Cabo
Verde Islands on Friday.

Maximum sustained winds are near 30 mph (45 km/h) with higher gusts.
Some strengthening is forecast during the next 48 hours, and the
disturbance is expected to become a topical storm during the next
day or so.

Environmental conditions are favorable for the system to become a
tropical cyclone tonight or Friday.
* Formation chance through 48 hours...high...80 percent
* Formation chance through 5 days...high...90 percent

The estimated minimum central pressure is 1007 mb (29.74 inches).


HAZARDS AFFECTING LAND
----------------------
RAINFALL:  The system could produce total rain accumulations
of 4 to 8 inches across the southern Cabo Verde Islands. These
rains could produce life-threatening flash floods.

WINDS: Tropical storm conditions are expected in the southern Cabo
Verde Islands on Friday.


NEXT ADVISORY
-------------
Next intermediate advisory at 200 PM AST.
Next complete advisory at 500 PM AST.

$$
Forecaster Avila

[yoda]

Potential Tropical Cyclone Six Discussion Number   1
NWS National Hurricane Center Miami FL       AL062018
1100 AM AST Thu Aug 30 2018

The area of low pressure that moved off the coast of Africa has
continued to become better organized, and is producing a large
area of disturbed weather with gusty winds, but currently lacks a
well-defined center.  Environmental conditions are favorable for
additional development, and a tropical depression or a tropical
storm could form an any time today or Friday.  Given the high
chances that this system could bring tropical storm conditions to a
portion of the southern Cabo Verde Islands, advisories have been
initiated on Potential Tropical Cyclone Six.  Most of the intensity
guidance calls for strengthening and so does the NHC forecast.

The system is embedded within the easterly trades and this flow
pattern will steer the disturbance toward the west or west-
northwest during the next few days.  By the end of the forecast
period, a turn toward the northwest should begin as the system
reaches a weakness in the subtropical high.  This is consistent with
the output of the global models.

FORECAST POSITIONS AND MAX WINDS

INIT  30/1500Z 12.9N  18.4W   25 KT  30 MPH...POTENTIAL TROP CYCLONE
 12H  31/0000Z 13.2N  20.1W   30 KT  35 MPH...TROPICAL DEPRESSION
 24H  31/1200Z 13.5N  22.0W   35 KT  40 MPH
 36H  01/0000Z 14.0N  24.0W   45 KT  50 MPH
 48H  01/1200Z 15.0N  27.0W   55 KT  65 MPH
 72H  02/1200Z 16.5N  33.0W   65 KT  75 MPH
 96H  03/1200Z 18.5N  38.0W   65 KT  75 MPH
120H  04/1200Z 20.0N  42.0W   65 KT  75 MPH

$$
Forecaster Avila

[WxWatcher007]

1 minute ago, yoda said:

Potential Tropical Cyclone Six Discussion Number   1
NWS National Hurricane Center Miami FL       AL062018
1100 AM AST Thu Aug 30 2018

The area of low pressure that moved off the coast of Africa has
continued to become better organized, and is producing a large
area of disturbed weather with gusty winds, but currently lacks a
well-defined center.  Environmental conditions are favorable for
additional development, and a tropical depression or a tropical
storm could form an any time today or Friday.  Given the high
chances that this system could bring tropical storm conditions to a
portion of the southern Cabo Verde Islands, advisories have been
initiated on Potential Tropical Cyclone Six.  Most of the intensity
guidance calls for strengthening and so does the NHC forecast.

The system is embedded within the easterly trades and this flow
pattern will steer the disturbance toward the west or west-
northwest during the next few days.  By the end of the forecast
period, a turn toward the northwest should begin as the system
reaches a weakness in the subtropical high.  This is consistent with
the output of the global models.

FORECAST POSITIONS AND MAX WINDS

INIT  30/1500Z 12.9N  18.4W   25 KT  30 MPH...POTENTIAL TROP CYCLONE
 12H  31/0000Z 13.2N  20.1W   30 KT  35 MPH...TROPICAL DEPRESSION
 24H  31/1200Z 13.5N  22.0W   35 KT  40 MPH
 36H  01/0000Z 14.0N  24.0W   45 KT  50 MPH
 48H  01/1200Z 15.0N  27.0W   55 KT  65 MPH
 72H  02/1200Z 16.5N  33.0W   65 KT  75 MPH
 96H  03/1200Z 18.5N  38.0W   65 KT  75 MPH
120H  04/1200Z 20.0N  42.0W   65 KT  75 MPH

$$
Forecaster Avila

Looks like the NHC is putting the breaks on the kind of rapid intensification we see on the guidance. 

[Windspeed]

Here is the 5km SST analysis for 08/29. The estimated location of the surface low is between the southern Cape Verdes and Senegal near the mouth of the River Gambia. SSTs are running around 28°C near to and just south of the Verdes to 27°C further west into the open Atlantic — good for initial development but only marginal on the future TC's forecast path.

The GFS OP was very bullish on its previous runs from 0z Wed through 06z Thur. However, the Thur 12z run has backed off rapid development into a hurricane within 36-48 hrs and now has slow strengthening into the MDR. The previous runs even had hurricane force in the southern Verdes, so that is good if the slower-paced development resolves.

I think this system does eventually become a hurricane into the central Atlantic, but I'm not as bullish in strength as the GFS has previously shown. The ECMWF has modeled a less favorable environment than the GFS and subsequently much slower development and only tropical storm intensity until it reaches the central Atlantic.

[WxWatcher007]

10 minutes ago, Windspeed said:

Here is the 5km SST analysis for 08/29. The estimated location of the surface low is between the southern Cape Verdes and Senegal near the mouth of the River Gambia. SSTs are running around 28°C near to and just south of the Verdes to 27°C further west into the open Atlantic — good for initial development but only marginal on the future TC's forecast path.

The GFS OP was very bullish on its previous runs from 0z Wed theough 06z Thur. However, the Thur 12z run has backed off rapid development into a hurricane within 36-48 hrs and now has slow strengthening into the MDR. The previous runs even had hurricane force in the southern Verdes, so that is good if the slower-paced development resolves.

I think this system probably does become a long-tracking hurricane into the central Atlantic, but not as bullish in strength as the GFS has previously shown. The ECMWF has modeled a less favorable environment than the GFS and subsequently much slower development and only tropical storm intensity until it reaches the central Atlantic.

That seems in line with looking at the overall conditions of the MDR and areas just north. Looking at both operational models, western portions of the MDR still look hostile for anything that develops close to the coast of Africa and tracks west. 

 

[Windspeed]

Very active surface trough extending into Senegal. You can see a more defined MCS with strong convection rotating around it near the mouth of the Gambia. From that location is likely where our LLC closes off over night or tomorrow. Additionally, the surface trough still extends well east into interior Africa, so we likley will have an active wave train in the coming weeks. Will be interesting to see how long this train lasts and also how far east the favorable MJO phase can extend to enhance the MDR somewhat.

[USCAPEWEATHERAF]

I think we will have a TD6 or Tropical Storm Florence earliest 2am and latest 5am later today.  I think Florence becomes a monster.

[yoda]

21 minutes ago, USCAPEWEATHERAF said:

I think we will have a TD6 or Tropical Storm Florence earliest 2am and latest 5am later today.  I think Florence becomes a monster.

Based off what?  And what is a monster?

[Windspeed]

Both the NHC and models have backed off faster development.

 

Visible satellite clearly shows counter-clockwise rotation at the surface with a the broad center now moving just south of Praia in the southern Verdes. You can see some low level swirls rotating north around that center. Did I say broad? The elongated surface low does look to have gained a little latitude over night, perhaps pivoting north around the surface trough and axis of monsoonal flow out of the ITCZ. Is that significant? Does not take much latitude gained to shift genesis and track into lower and marginal SSTs. More importantly, the sheer size of the surface low at this time is going to be responsible for slow development. I am not saying this won't eventually become a TC. We have had plenty similarly large surface lows enter the MDR and become hurricanes, especially in active years. It's just the MDR has not been all that favorable so far. And though it may become more favorable in the coming weeks, this particular potential TC may be a little early for that and struggle.

[WxWatcher007]

Everything has been a struggle so far in the basin. Meanwhile, the PAC is on fire. 

[Windspeed]

 

848

WTNT41KNHC 312033

TCDAT1

Tropical Depression Six Discussion Number 6

NWS National Hurricane Center Miami FL

AL062018

500 PM AST Fri Aug 31 2018

High resolution satellite images reveal that the disturbance has developed a well-defined circulation with a cyclonically curved convective band near the center, and plenty of showers in the southern semicircle. The surface pressure in the Cabo Verde Island of Santiago dropped to 1005 mb at 1800 UTC as the cyclone passed to its south. In addition, Dvorak numbers are gradually increasing, and now support classifying the system as a tropical depression.

The depression is becoming better organized, and it will most likely reach tropical storm status in the next several hours. The environmental conditions are favorable for some strengthening during the next 2 to 3 days while the shear is low. Later in the forecast period, the shear is expected to increase, and the SSTs will become marginal halting the strengthing process. The models, primarily the HWRF, are a little less aggressive with the intensity, so the NHC forecast is adjusted slightly downward.

Now that the center has formed, we have a better estimate of the initial motion, which is toward the west or 270 degrees at 13 kt. The depression is gradually becoming steered by the flow around the subtropical ridge, and consequently it has increased its forward speed. This prevailing flow pattern should keep the cyclone on a general west to west-northwest track for the next 2 to 3 days. After that time, a weakness in the ridge will induce a more northwestward to north-northwestward track over the open Atlantic Ocean. The track guidance is very consistent with this solution mainly for the next 3 days. Thereafter, the confidence in the track forecast decreases as the guidance envelope widens and becomes bounded by the westernmost ECMWF and the easternmost HWFI. The NHC forecast continues to be in the middle of the envelope and is very close to the corrected consensus HCCA, which has had great skill so far this year.

FORECAST POSITIONS AND MAX WINDS

INIT 31/2100Z 13.8N 24.7W 30 KT 35 MPH

12H 01/0600Z 14.3N 26.7W 35 KT 40 MPH

24H 01/1800Z 14.9N 29.2W 40 KT 45 MPH

36H 02/0600Z 15.8N 31.8W 45 KT 50 MPH

48H 02/1800Z 16.5N 34.5W 50 KT 60 MPH

72H 03/1800Z 18.0N 39.5W 55 KT 65 MPH

96H 04/1800Z 20.0N 44.0W 60 KT 70 MPH

120H 05/1800Z 23.0N 48.0W 55 KT 65 MPH

$$ Forecaster Avila

Edit: Code.

[USCAPEWEATHERAF]

23 hours ago, yoda said:

Based off what?  And what is a monster?

Major Hurricane status

[yoda]

1 minute ago, USCAPEWEATHERAF said:

Major Hurricane status

And as you can see NHC has Florence not even making hurricane status... major hurricane LOL

[Windspeed]

Saturday 0z ECMWF has a big change. Though it continues to pummel future Florence at the 400-300mb level across the MDR, keeping it much weaker and steered further west into the surface flow and trades, it also models the pattern differently. Florence survives and is gifted strong 500 mb heights right over Bermuda and the NW Atlantic, with a nice upper ridge right over top. With that setup, unsurprisingly, Florence rebounds and becomes a formidable hurricane well north of the Greater Antilles moving WNW. That's 200 hrs out, mind you, and the first run with a big shift in potential track, so view it with caution and a grain of salt. We'll see if the 12z ECMWF is also onto something or this is just a blurp.

 

[shaggy]

3 hours ago, Windspeed said:

Saturday 0z ECMWF has a big change. Though it continues to pummel future Florence at the 400-300mb level across the MDR, keeping it much weaker and steered further west into the surface flow and trades, it also models the pattern differently. Florence survives and is gifted strong 500 mb heights right over Bermuda and the NW Atlantic, with a nice upper ridge right over top. With that setup, unsurprisingly, Florence rebounds and becomes a formidable hurricane well north of the Greater Antilles moving WNW. That's 200 hrs out, mind you, and the first run with a big shift in potential track, so view it with caution and a grain of salt. We'll see if the 12z ECMWF is also onto something or this is just a blurp.

 

That's a big shift in one run. It's the euro so certainly cant be ignored but it would need several runs and some serious support from the other models. It will be interesting to see what the ukmet does as time goes on. It did pretty good last season.

[fountainguy97]

Euro run is very strange. Has Florence at TD/weak TS status for the next 168hrs.  On tidbits the highest 850mb winds I find in that time frame are 46knts..   

 

i find  it hard to believe that Florence stays THAT weak. 

 

Especially since i see a Dvorak ADT up to 3.5 with winds of 55knts. 

[shaggy]

23 minutes ago, fountainguy97 said:

Euro run is very strange. Has Florence at TD/weak TS status for the next 168hrs.  On tidbits the highest 850mb winds I find in that time frame are 46knts..   

 

i find  it hard to believe that Florence stays THAT weak. 

 

Especially since i see a Dvorak ADT up to 3.5 with winds of 55knts. 

06z gfs also had a noticable shift west from its 0z run. Still recurves east of Bermuda though.

[Windspeed]

12z GFS does a similar thing as 0z ECMWF with Florence, keeping upper level conditions less favorable and a weaker TC initially across the MDR; therefore, it is more steered by 850-700 mb flow and further west than previous GFS runs. However, it still differs greatly on pattern beyond 5 days. ECMWF builds heights over NW Atlantic and allows Florence to slip under it. GFS not so much, stalls Florence, then eventually continues to lift Florence up and out east of Bermuda. But we'll see if the 0z ECMWF was merely a blurp in the next hour when the 12z is out.

 

 

 

 

 

[Snow88]

Dt thinks might not miss ots

[Windspeed]

Thinking the 0z ECMWF was just a hiccup. 12z is back on a stronger central Atlantic weakeness and trough.

[Snow88]

17 hours ago, Windspeed said:

Thinking the 0z ECMWF was just a hiccup. 12z is back on a stronger central Atlantic weakeness and trough.

0z Euro has the ridge building. Closer to the U.S. on this run.

[NutleyBlizzard]

22 minutes ago, Snow88 said:

0z Euro has the ridge building. Closer to the U.S. on this run.

Still a long way out, but looking at the Euro's perspective of the 500mb map you have a pressing ridge with no kickers in sight so there's really nothing from stopping Florence eventually making a Mid-Atlantic/NE coast landfall. 

[shaggy]

On ‎9‎/‎1‎/‎2018 at 7:49 AM, fountainguy97 said:

Euro run is very strange. Has Florence at TD/weak TS status for the next 168hrs.  On tidbits the highest 850mb winds I find in that time frame are 46knts..   

 

i find  it hard to believe that Florence stays THAT weak. 

 

Especially since i see a Dvorak ADT up to 3.5 with winds of 55knts. 

She is weakening now and the NHC is shifting track further south and west to match up closer to the Euro and Ukmet models. Maybe the euro track is onto something with her weakening already.

[csnavywx]

The issue is marginal SSTs in the near term and wind shear in the longer term when she gets back over warmer SSTs. There's consistent consensus of about 15-25 knots of wind shear past about 72-96 hours that will hinder strength as well. These issues might be alleviated if it misses the trough at day 6/7 and gets tucked under the ridge as SSTs in the subtropical Atlantic are running well above normal and wind shear would likely abate in that case. The massive upstream wave break caused by STY Jebi's recurve and interaction with mid-latitude westerlies will probably alter the environment for a future Florence track if it misses the trough too.

[shaggy]

CMC has certainly changed from the last run. From a way east recurve to having a cane threatening the east coast. So maybe a 1000 mile shift west in one run. To say the long range with this one is complicated is an understatement.

[Vice-Regent]

[The run]

[purduewx80]

12Z GEM and ECM nearly on top of each other at D10 near the Outer Banks. GEM ensemble mean is farther S. Curious to see the 12Z EPS. 

[Windspeed]

Good lord, if that isn't a Mid-Atlantic/Delmarva weenie run, I don't know what possible could be...

Notice the 500 mb heights at the end of that run. That's a block-a-roo and would drive Florence well inland. Still much caution though, this is 200 hrs out and low confidence.

[csnavywx]

In the shorter run, the storm nearly gets ripped apart by wind shear on that run. The surface low opens up into a wave and the mid-level vortex barely survives before getting into favorable conditions and regenerating. A system that weak will easily miss the first trough and stay south. If it is stronger than forecast though, it could get picked up or deviated far enough to the right to still put it out to sea. The CMC also keeps it fairly weak and ends up with nearly the same solution.