Ex Hurricane Leslie Update

Update 8th Aug 20.00hrs (GMT)

Her failure to intensify while stationary as originally predicted limits the southerly swell from this stage of the storm, although a further pulse later in the week is possible.

Leslie was originally predicted to grow and intensify while moving slowly spitting swell in all directions with a peak as she reached maximum size. With her complete lack of movement cooling seas and hindering her growth this later peak is now looking less likely for areas south of the storm, she will intensify as she moves north over warmer water but her forward motion will limit southerly swell development. Although later on than originally expected a developing southerly fetch as the storm reaches Nova Scotia might send a second pulse towards Florida for a mid week bump.

That said the stall is still meaning we have a prolonged swell event from this storm, with moderate long period swell on tap right up to the middle of next week.

The second storm models were seeing at the start of last week is now a clearly visible tropical wave on the latest satellite images and the NHC see a 40% chance of a storm in the next 48hrs.


Dillon Murphy blasting an air reverse up on Cape Cod thanks to Hurricane Leslie Credit: Trevor Murphy

Update: Fri 7th 16.00hrs (GMT)

LESLIE has spent so much time messing about she’s really hurting herself, cooling the sea to such an extent that she’s lost Hurricane status. An approaching trough pushing her north should give her the opportunity to find the energy she needs to regain Hurricane form. Outlook for swell remains positive, although the peak is pushed back a little and peak numbers cooled slightly on previous outlooks.

Florida

Continuing mid sized swell peaking later in the weekend/Monday then again potentially in the middle of next week as a broad weaker fetch develops sending swell south, but allowing for accompanying onshore winds.

Outer Banks

Swell peaking again on monday but the same developing NE wind flow and continuing mid sized longer period swell well into the middle of next week and beyond.

NJ/NY

Swell peaking on Monday with a fresh northerly airflow bringing offshore winds to Long Island.

New England

Getting the best of it with a strong pulse on monday and offshore winds.


Update: Thurs 6th 13.30hrs (GMT)

Some change overnight with Leslie becoming a fully fledged Hurricane. The general outlook remains similar with swell peaking over the weekend although the prognosis for Europe is changing with each update. The follow on storm we mentioned yesterday looks set to form (or not) over the weekend too so we could have three systems in play in the Atlantic by next week.

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Hurricane Leslie is now a Hurricane but her reluctance to jog on northwards means she’s failing to intensify as fast as she could. Hurricane’s fuel themselves with warm, moist air. Leslie’s spent so long hanging around in the same place she’s started to stir up the ocean and this deeper, colder water has dropped sea temperatures causing her some growing pains. This situation should remedy itself once she starts to move north over the next few days.

GOES Satellite Image (c) NASA

For Europe the outlook changes fairly significantly as indications of a south/north jetstream potentially push the system into Greenland rather than straight east across the Atlantic. A change of this magnitude since yesterdays model runs gives and idea of the variability possible in this time range. However both scenarios allow for European swell from the Ex-Hurricane system in almost a fortnights time. Additionally most of Europe should see a small long period swell from the current hurricane phase in around a weeks time if things develop as expected.

Major Hurricane Michael is the most powerful storm of the season so far but small and on a track that’ll add little to the coasts likely impacted by any swell produced, given the proximity of Leslie over the same period.

Beyond this the GFS, ECMWF and UKMO models are all very keen on the development of a new Tropical Storm system off the coast of West Africa over the weekend taking a track of interest for the US East coast.


Update: Wed 5th 9.35hrs (GMT)

Essentially no change to the outlook. Continued positive forecast for surf for all coasts in the basin peaking over the weekend as the storm grows and strengthens.

Monday 10th September significant wave heights. (c) MSW

The NHC are still anticipating a reduced wind shear in the next 24hrs allowing the already large storm to slowly grow in size and strength with a 72% chance of Hurricane status by next week. As important as the strength for this storm it’s the size that looks exceptional and it remains this, coupled with the slow track that looks likely to deliver a prolonged blast of long period swell in all directions. Essentially no change from the original outlook for surf below – use the local links for specifics in your area.

European Outlook

Long range charts are still showing potential for the storm becoming an extremely substantial cold core system as it transits via Nova Scotia into cold water intercepting a strong west/east jetstream. While we have to urge caution as always at this range there’s is some consensus among global models for this scenario:


Update: Tues 4th 20.00hrs (GMT)

TS Leslie is currently heading North at about three knots – you could probably out paddle her if she’d let you close enough…

Latest Buoy Readings are in the 4ft@15 seconds range from North Carolina all the way to New England and just slightly shy of this further south to Florida with waves already in the head high+ range along the coast.

Swell looks to be increasing (albeit relatively slowly) on all exposed coasts. Outlook remains as before with this pulse to peak tomorrow while a building but stalled storm continues to send swell to all exposed coastlines peaking again as the storm reaches it’s forecast maximum size later in the week. Largest in regions north of the storm system as it moves in that direction but numbers later in the weekend almost twice that of today’s even in Florida.

The Caribbean is, bizarrely, going to see it’s best swell from this storm as it grows and trundles slowly north, rather than as it passed by the first time. Solid long period swell running into and over the weekend peaking in a similar range of around 8ft@14 seconds in Puerto Rico as an example from the latest model forecast.


While Leslie still hasn’t achieved Hurricane status she’s been producing a good quantity of swell, crucially heading in the right direction for surfers from Florida to Nova Scotia. The outlook for further swell generation remains broadly as originally forecast and with swell already heading towards exposed coasts a prolonged event starting on Tuesday 4th should have surfers already waxing up.

The image below shows the recent track of Leslie in black, with the red lines giving a rough idea of the great circle propogation of swell from the inital direction and since the turn northwards. Areas within and around these red lines, from Florida to Nova Scotia are set to receive swell already propogating. A quick check of the nearby wave buoys shows 11.5ft@14 seconds on the lower end of the window, and a more robust 13.8ft@14 seconds on the more northerly end – as a result of the increasing strength and proximity to the storm centre.

TS Leslie's track and lines showing the path of propagation from the recent track. Wave buoys with readings from Mon 3rd 9:00 GMT are show in yellow.

All this means regardless of the forecast for the future of the storm we’re already guaranteed swell on exposed coasts with the model forecast predicting the early stages on Tuesday 4th August and as early as today on the OBX. Further on a stalled storm increasing in size means the strong possibility of a prolonged swell event with surf actually peaking later in the week (particularly for Northern states benefiting from the change in track) and potentially running all the way through to Tuesday next week or even beyond. If it does develop in line with the broad consensus of model possibilities then, while this storm might not hit the big numbers of previous seasons stand out storms (particularly in the south) it’ll could actually see more decent waves ridden by more surfers than most storms in recent memory due to it’s predicted stall and size.

Surf Outlook*

Florida – South Carolina

Swell arriving early on Tuesday 4th building to 3.5ft@14 seconds during the day (Head+ waves on the better exposures) with light winds tending onshore in the afternoon. This pulse from the initial storm path peaks on Wednesday morning. The model then shows pulses of swell in this size range all week and, if the storm increases in size as the model expects, a stronger peak towards next weekend possibly pushing wave size  into the head and a half to double over range at the best spots although potentially coupled with some stronger winds blowing cross/onshore at times.

Latest Florida Hurricane Swell Forecast

Outer Banks

Swell pushing in this evening (3rd) and building through to a solid 6ft@14 seconds on wednesday (head and a half to double over on the best banks/exposures) and remaining solid all week potentially pushing larger still later in the weekend if the storm intensifies on plan. Moderate to strong south westerly winds for the entire forecast period will favour east or better still north east facing coastline.

Latest Outer Banks Hurricane Swell Forecast

New Jersey / New York / New England

Swell arriving tuesday morning and building into the 2-4ft@14 second range (head high+ at the better spots) but with south westerly winds increasing to strong particularly on wednesday and affecting spots exposed, particularly the Long Island coastline. Winds are lighter further north in New England. Strong pulses all week with the wind easing and, if the model outlook is correct, the storms increasing size and favourable track means the possibility of a considerable bump in size for later on in the weekend with the latest (and potentially less reliable at this stage) numbers in the 8ft@16seconds range – which’ll mean waxing up the bigger boards and finding the spots that can handle a bit of juice.

Latest NJ/NY Hurricane Swell Forecast

Nova Scotia

Swell arriving Tuesday and building throughout the week as the storm increases in size and moves toward a potential landfall scenario. Winds an issues wednesday/thursday for affected spots and, obviously, should the storm continue on a northerly track!

Latest Nova Scotia Hurricane Swell Forecast

Europe

As it stands this storm has had limited fetch to create meaningful swell for Europe. Over the next few days a larger storm on a northerly track will create a very modestly sized long period swell for the middle of next week. A more interesting scenario is a development of the storm into a large cold core system as it moves north over the Canadian coast, hitting a favourable jetstream and moving east. This is a long range, low probability possibility but one to keep an eye on.

* Outlook is based on NAH hurricane swell model data and is a useful guide, particularly for this larger storm, however gridded models have well documented issues resolving the peak swell from Hurricane systems and should, of course, be used as a guide. Outlook in the next 48-72hrs is based largely on swell already propagating and can be considered reliable, beyond this predictions are based themselves on assumptions of the storms development. There’s a good model confidence in the latest scenario for the timeframe beyond this but, as always, it’s subject to change.