First, where have we been...
Here's the trend from the last 8 runs of the GFS. Until yesterday's late run, it kept it well at sea.
This was the initial forecast
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
TD Six was hatched on the 31st on the 21z advisory
That Forecast discussion maxed it out a 70mph.
TS Florence was named in the 5 am advisory on the 1st.
Still the 5am forecast disco kept it at under Hurricane strength through day 4
For all of Sept 3rd she remained at 65-70mph speed until the 11am advisory on the 4th when she became a hurricane.
Hurricane Florence Advisory Number 21 NWS National Hurricane Center Miami FL AL062018 1100 AM AST Tue Sep 04 2018 ...FLORENCE BECOMES THE THIRD HURRICANE OF THE ATLANTIC SEASON... ...NO THREAT TO LAND THROUGH THE WEEKEND... SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION ----------------------------------------------- LOCATION...19.7N 42.5W ABOUT 1240 MI...2000 KM WNW OF THE CABO VERDE ISLANDS ABOUT 1270 MI...2045 KM ENE OF THE LESSER ANTILLES MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H PRESENT MOVEMENT...WNW OR 295 DEGREES AT 12 MPH...19 KM/H MINIMUM CENTRAL PRESSURE...990 MB...29.24 INCHES
11am ast disco mentions that the shear would knock her back to TS and then gain to H by 9th. The track was uncertain though it clearly looked to be headed east of Bermuda and highly unlikely to make a US landfall.
This analysis didn't work out. by 2pmAST she was 85mph. By 11pm advisory she was 100mph. And at 8:30 AST they advised she was Cat 3, 120mph at 961mb. Intermediate advisory
So that takes us to the 11am Disco which adjusts the track west, but is highly uncertain, and not as far west as the models. The analysis shows that a pocket of low shear allowed her to develop, but that the shear should increase and knock her down again.
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
The GFS was really the last hold out as even the NHC ensembles are further west.
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| 6z NHC |
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| 12z nhc |
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| 9-3 0z euro ens |
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| 9-3 0z ukmet ens
Thoughts on the ridge/trough and other features that would affect this are at wxdisco
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