2018 Hurricane season - bring back the sand...
Tuesday 9th September 2018
It's hard to think that less than two weeks ago, we were twiddling our thumbs watching a stream of fledgling systems disappearing into Saharan sand across the convergence zone. I try to keep these bulletins as brief as I can, but today the reporting zone is bubbling like a cauldron and there is much to report.
We have six pressure systems seaborne, two hurricanes, one tropical storm, two disturbances with ambition and a new launch shortly leaving the African coast. So, from west to east -
Disturbance Thirty Six is currently transiting the Yucatan Channel, headed into the Gulf of Mexico on a north-westerly heading making about 8 knots. At present, this is little more than a swirl of squalls radiating out from the nominal centre over a fairly limited radius. This is being kept in place by upper level shear, however this has started to weaken and may allow vertical convection and surface circulation to develop. If this does develop, it has limited prospects and may struggle to reach beyond an average tropical storm. The current track has this making a landfall around Corpus Christi overnight on Thursday. Irrespective of development, this will bring heavy rain to the Texas coast. For those who must, the peak hurricane severity rating (if this develops) at landfall is just 3 out of a possible 50 (1 for size and 2 for intensity).
I doubt anyone is short of updates on Hurricane FLORENCE. When conservative commentators use terms such as ‘extremely dangerous', ‘widespread catastrophic flooding' and ‘threat to life', we know we have a significant powerful hurricane on our hands. Currently 1,000 miles east of Cape Fear, North Carolina and headed west-nor'west at 12 knots, FLORENCE has a current hurricane severity index rating of 25 (9 for size and 16 for intensity) with a tropical storm force windfield radius of 125 miles and is producing steady winds of 120 to 140 knots. Unfortunately, intensification is set to continue and this will reach category five tomorrow. There is a slight chance of upper level shear taking the edge off this as it approaches the eastern seaboard but will do little more than reduce intensity from category 5 to 4, I'm afraid. To make matters worse, there is some argument for FLORENCE stalling as it nears the coast which would considerably increase precipitation and flooding, as the cyclone would effectively then siphon sea water and simultaneously deposit it ashore. At peak, a maximum hurricane severity index rating of 36 out of a possible 50 points (16 size, 20 intensity) is predicted. This has increased by three points in the last hour since receipt of a report from an aerial reconnaissance aircraft in the last hour. As to landfall, depending on the impact of stalling and a small wobble to the west which has also been picked up in the last hour, this may be as late as overnight on Friday in North Carolina with ‘considerable' rainfall and a ‘very significant' storm surge.
Tropical storm ISAAC is centred 750 miles east of the Windward Islands, westbound at 12 knots. This is expected to intensify to hurricane strength then weaken again before landfall as it encounters upper level shear. This has a current hurricane severity index rating of 6 (2 size, 4 intensity) which will probably be the same at landfall, with a tropical storm force windfield of 60 miles. Fortunately this remains a tiny storm and as such, offers some hope of limited impact. ISAAC is expected to make landfall over the central Lesser Antilles as a strong tropical storm on Thursday, thereafter weakening quickly as it enters the Caribbean.
Hurricane HELENE is not presenting too many problems. Currently centred 500 miles west-sou'west of the Cape Verde Islands, this has curved onto a west-nor'westerly heading and is making 10 knots. This is now a category two hurricane producing 95 knot winds and is expected to peak at category three tomorrow. Thereafter gradual weakening is expected. There is a slight chance that this could reach the Azores, but a little early to call just now.
Well to the north, Disturbance Thirty has developed to the west of the Azores. Some slow subtropical or tropical development is possible with the system later this week as it moves to the south-west but this will not approach any land mass.
Disturbance Thirty Eight is emerging from the African coast and is expected to be seaborne soon. There's enough to worry us much nearer to home, so we'll take a shufti at this tomorrow, if that's OK.
Bring back the sand…