A new phase to the 2014 storm season taking shape. Stand by Gulf of Mexico?
A slightly more detailed review today, as there are significant changes to the storm season profile in the coming weeks which are worthy of mention. For the speed reader who only wants to see the daily analysis, the next four paragraphs will be all you need.
Disturbance seventeen is in the southern Bay of Campeche moving west at 18 knots and will be high and dry in a few hours.
Disturbance nineteen is now centred around 500 miles north of the Amazon delta headed west at 10 knots. Disturbance twenty is just under a day's steaming astern of it and has about an eight knot advantage. It is possible that these could merge as they approach the Lesser Antilles. Conditions across the Atlantic basin are changing and becoming more attractive to storm formation. Merging pressure systems sometimes behave erratically, so forward motion and intensity are unpredictable but a number of combinations are offered, of which more detail is given below. Nineteen will certainly be approaching the Lesser Antilles by Friday. Unhindered by the pursuing disturbance twenty, one would expect this to enter the Caribbean as a tropical wave, but with the impending merger, all such bets are off.
Disturbance twenty-one still looks keen. This is just passing the Cape Verde islands and is moving west at 15 knots.
There is still talk of a trough of low pressure off the southeast coast of the United States or near northern Florida in about a week from now which may develop into a weak tropical cyclone. I can't see it, but better men than I assure me it will happen.
Now, for a more rambling monologue.
Conditions in the central and eastern Atlantic have become a little more favourable for cyclonic development this week. This is certainly the start of a more active period of the storm season. There are three fledgling systems under way today, and a tour of the regular modellers shows a majority view that this triplet includes tropical storm CRISTOBAL.
I routinely look at a number of models. I prefer to focus on US and European commercial meteorological analysts, who routinely prove to be the most reliable, a Canadian observer, less reliable with a tendency to lean towards catastrophic forecasts and always good for a laugh, and a US Navy source which, although lacks the gloomy storm enthusiasm of the Canadian, is marginally less dependable but still ahead of the rest of the global pack.
Taking the three systems at large today, in reverse order of model reliability -
The US Navy modeller is not always reliable in reading the Atlantic basin. This analyst has the three systems producing two storms next week, CRISTOBAL and DOLLY, both clipping the north east islands of the Caribbean – both turning to the north west, then north. One likely to pass close to and perhaps make a landfall in Florida, and the other to pass offshore.
The Canadian model is entirely different and has a cyclone developing at the end of the week, which will become a ‘fairly strong' tropical storm CRISTOBAL by the beginning of next week in the central Caribbean. This will then enter the southern Gulf of Mexico/Bay of Campeche by Wednesday or Thursday of next week.
The US and European modellers have not been quick to hang their hats on CRISTOBAL, but have two of the three systems heading into the Caribbean as tropical waves, following the Canadian track, which has been the pattern over the last few weeks. Within the groups of modellers however, individual opinions are beginning to waver and it is possible that one or more of the A* analysts will nod closer towards the Canadian model.
The maps of current and predicted wind shear for today and next week show dramatic changes and conditions at higher altitude which have been adverse for several weeks. These are beginning to show large areas of undisturbed air, particularly over the western Caribbean and Gulf of Mexico. To add to this, the Madden-Julian Oscillation, which is a slow moving undulation in atmospheric convection which parked sinking air over the Caribbean and Gulf of Mexico for some time, is shifting and will reverse over the next fortnight. Rising air is perfect for storm formation.
Whilst frontal activity has been fairly active, this has essentially been driven by three predominant pressure gradients. A low pressure area offshore between Cape Cod and Cape Hatteras, a high pressure cell over the southern states between the Mississippi and northern Florida, and a second high pressure area to the east-sou'east of Bermuda. This array was the driving influence for ARTHUR and BERTHA to pass between the highs, head for the low and swipe the eastern seaboard. This configuration is changing and will be replaced by an elongated high pressure ridge centred over Bermuda and extending west into the north eastern Gulf of Mexico from now until the second week of September. This will guide cyclones to the western Caribbean and Gulf of Mexico.
In the short to medium term then-
We can expect cyclone friendly conditions from now until at least the second week in September and this could produce between three and five named storms over the next month.
Conditions which have been defending the central Caribbean and Gulf of Mexico have eased. Systems from the convergence zone which successfully cross the Atlantic are more likely to head west towards the western Caribbean and Gulf of Mexico.
On the positive side, analysts are watching the El Nino closely. There is a strong possibility that this may put a damper on the season and one or two hopefuls are already suggesting a very early end to the 2014 season, perhaps as early as the first or second week of October.
Stand by Gulf of Mexico?