A busy day across the region, but most eyes on FLORENCE

Wednesday 12th September 2018

All eyes are currently on FLORENCE, so let's deal with the other runners and riders first. From west to east:

Disturbance Thirty Six is now 485 miles east-sou'east of Corpus Christi headed north-west at 8 knots. This has not really dug in much since this time yesterday but does look set to intensify. The reduced ground speed is disappointing since this will allow development time and whilst this has been earmarked as a potential tropical storm for the past couple of days, delays at sea may mean further intensification. As things stand, this look set to hit the beach somewhere close to Corpus Christi on Friday. As this crosses the offshore leases beginning tomorrow morning this is expected to have a peak hurricane severity index rating of just 3 of a possible 50 (1 for size and 2 for intensity) so as tropical storms go, this is likely to be a runt. Hopefully. Having said that, this will still mean wind gusts up to 55 knots with heavy rain in squalls across coastal areas of Texas and some high seas.

Caribbean-bound Tropical Storm ISAAC is 430 miles east of the northernmost Windward Islands headed west at 15 knots. This is at peak now with a hurricane severity index rating of 5 (2 size, 3 intensity) with a tropical storm windfield radius of 80 miles. ISAAC is expected to make a landfall ‘as is' tomorrow morning with 55 knot winds. In my view, the convection profile of ISAAC is slightly skew-whiff with its low-level circulation axis racing ahead of the nominal squall centre and mid-level circulation leaning east, which would hint at an eleventh hour weakening, however this doesn't seem to be shared by the professional agencies. We can however expect upper level wind shear to come to the rescue after landfall as this tracks into the Caribbean.

Well to the north, Disturbance Thirty Seven is loafing about a couple of hundred miles west of the Azores producing a large sweep of showers and thunderstorms with some gale force winds. We are watching this because subtropical or tropical development is possible as it moves south-west, but will probably only bother fish and sailors.

Category 2 Hurricane HELENE is around 1350 miles south-sou'west of the Azores and moving north-nor'west at 12 knots and showing signs of weakening with maximum winds down to 85 knots. One or two modellers are indicating that HELENE will reintensify as it moves through the Azores in about 4 days' time.

New Disturbance Thirty Eight is passing close to the east of the Cape Verde Islands with some heavy showers and thunderstorms, westbound at 8 knots. This is yet to show any organisation but it's early days.

So, to FLORENCE. Category 4 Hurricane Florence is located about 570 miles to the east-sou'east of Cape Fear, North Carolina and is moving to the north-west at 15 knots. This has a current hurricane severity index rating of 28 (12 for size and 16 for intensity) and a tropical storm windfield radius of 160 miles producing wind gusts up to 145 knots. I won't cloud the summary with descriptions of eyewall replacement as our main concerns now are when, where and how hard. There is some chatter of a wobble but far from certain. In any event, the problem we have with deciding impact is the increasing fear that this storm is going to stop dead just before or near to landfall, which will add multiples to any storm surge, rainfall and wind duration forecasts. At that time, FLORENCE will have a hurricane severity index rating of 30 (14 for size and 16 for intensity) with a tropical storm windfield radius of 180 miles,

Where? On its current heading, FLORENCE would be expected to land near Cape Fear early on Friday morning however, any reduction in speed is likely to push FLORENCE south, anywhere between Charleston and Myrtle Beach.

When? If this doesn't stall, then it will make a landfall on Friday morning. If it stalls, or tracks more to the west at slow speed, this could be much later.

How hard? Catastrophic hurricane force winds and tidal surge damage up to 12 feet in places are expected for the North Carolina coast, with severe flooding for North and South Carolina. If this tracks south, the threat could extend as far as Georgia. This is a nasty, nasty storm.

Stand by for tropical storm conditions in the northern Leeward Islands and for the early signs of FLORENCE on the coast of the Carolinas. 

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