Will we see yet another active tropical storm season in 2018?

Hurricanes have no respect for humans or their calendars. The traditionally designated “hurricane season” in the Atlantic runs from June 1st to November 31st but named storms have developed as soon as January (Hurricane Alex on 12th January 2016). The latest date for the first storm to be named was 31st August 1967 (Hurricane Arlene).

So far in 2018 we have had one named Atlantic storm, actually in the Gulf of Mexico. This was Subtropical Storm Alberto which drifted northwards to make landfall over the Florida Panhandle on May 28th. Its winds never made hurricane strength but it brought some damaging gusts and exceedingly heavy rain and floods. The effects were felt over a wide area of the eastern USA as it trundled far north, reaching the Great Lakes region before dissipating.

Subtropical Storm Alberto crossing the coast of the Florida Panhandle. Image courtesy of NASA.

It’s pretty rare for a subtropical or tropical system to retain its characteristics that far north having crossed so much land but it was fuelled partially by something called the “brown ocean effect”, whereby storms derive their energy not from the ocean as usual but from the evaporation into warm air of abundant moisture in the soil. Alberto contributed to devastating flooding as far away as Ellicott City, Maryland, as its outer rain bands fed constant thunderstorms across the state.

But what of the rest of the year? How active is the Atlantic likely to be between now and late autumn? Most early predictions were predicting an above-average number of named tropical storms (a broad consensus of about 13 to 15 in total) and hurricanes (around 6 or 7 including a risk of about 3 major hurricanes). These predictions were partly driven by noting unusually warm waters in the western tropical Atlantic and the Gulf of Mexico and no expectation of El Niño development this summer or autumn.

Although it is a tropical Pacific phenomenon, El Niño is associated with strong high-level winds across the Caribbean and tropical Atlantic. A strong increase of wind speed with height (“shear”) can tear storms apart before they have time to strengthen. Hurricanes thrive when weak upper winds allow them to grow. So warm seas and favourable winds should on the face of it mean a relatively active season.

However, MeteoGroup’s partners at the World Climate Service (WCS) take a different view and are predicting below-normal tropical cyclone activity. Why such a difference in the prediction? Firstly, it’s important to note that hurricane outlooks for an entire season generally have low confidence in any case, particularly years like this in which there are no strong climate signals – unlike in 2017, the costliest in history, when there was justified confidence in forecasting an active and, as it turned out, very destructive season. Secondly, although MeteoGroup and the WCS recognise the aforementioned factors that could contribute to energetic developments there are several other considerations that give pause for thought.

Tracks of 2017’s tropical cyclones & hurricanes, courtesy of the National Hurricane Center (NHC) and NASA.

One of those is that El Niño is not the only influence on wind strength above the Atlantic. There is an oceanic-atmospheric pattern called the North Pacific Mode which is expected to be in its positive phase, and this correlates with strong wind shear across the Atlantic Main Development Region (MDR), with the last several years showing a strong connection.

Although the western tropical Atlantic and the Gulf of Mexico are unusually warm the eastern half of the ocean is cooler than normal. Indeed, the WCS notes that the ECMWF seasonal forecast for August sea surface temperatures in the MDR would put them at some of the coolest on record. This is significant because the seeds of many hurricanes are sown off West Africa near Cabo Verde (Cape Verde). A lack of energy there could stifle these developments. The same forecast also carries a strong signal for rather dry conditions in the tropical Atlantic through summer and early autumn, and so does NOAA’s CFSv2 seasonal model.

Wind and precipitation forecasts from the CFSv2 seasonal model for August-October 2018, coutesy of the World Climate Service.

Moreover, we have recently seen an extensive high pressure ridge in the sub-tropics draw dry and dust-laden air off the Sahara and carry it thousands of miles westwards across the Atlantic, and dry, dusty layers in the atmosphere are known to inhibit hurricane development. It’s worth noting that several other agencies have in early June adjusted their expectations slightly downwards. 

Satellite image courtesy of NOAA

Sea surface temperatures reach their peak in September and October so it is possible that there will be an uptick in development later in the season across the Atlantic. Until then the focus could be on potential activity in the Caribbean and Gulf of Mexico where seas are already very warm. Alberto might have set the tone for at least the first part of the season but predictions of dry conditions spread to the Caribbean so even that becomes more doubtful.

These broad predictions, as with other seasonal outlooks, can be a useful indicator for mitigation planning but inherently lack specifics. When it comes to the nitty gritty of dealing with an actual developing tropical cyclone or hurricane then short-term forecasts become essential, especially at sea. MeteoGroup offers a suite of products especially for the Offshore industry, from coastal eengineering, to subsea construction and oli & gas exploration, providing you with local weather and metocean data in great detail. In addition MeteoGroup offers a suite of services and products that can not only keep seafarers safe but also save fuel and reduce emissions by assisting the most efficient navigation around these hazards.

RouteGuard, for example, identifies the most efficient routes commensurate with safety, and allows captains owners and vessel managers to not only pre-plan a voyage but adjust en route and also produce post-voyage analyses. RouteGuard is driven by data, not only meteorological but including consideration of currents, tides and wave direction, but dovetails with the deep experience of MeteoGroup’s Shipping Operations team. In addition, to comply with emissions regulations, over 100 shipping companies use our FleetGuard system, which monitors and reports on each ship and every voyage. 

Routing around a tropical storm, a safe distance of at least 300 miles from the centre is assumed but advice from Shipping Operations will depend on the type of vessel and whether or not it is able on a tight schedule to slow or even stop. Standard forecasts are five days ahead but for hurricanes they are more likely to focus on the first two to three 3 days due to their dangerous changeability, with regular updates every six to twelve hours.

Over 2,000 clients worldwide use the on board SPOS software (Ship Performance Optimisation System), driven by MeteoGroup’s own in-house model, the Nautical MeteoBase. SPOS allows captains and crews to adjust route calculations and plot optimum routes depending on updated weather information, while most efficiently navigating and, most importantly, keeping all hands safe from the threat of storms and hurricanes, however many we might see this year.

Stephen Davenport
Senior Meteorologist / Energy Meteorologist
MeteoGroup USA.

 

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Sea surface temperatures reach their peak in September and October so it is possible that there will be an uptick in development later in the season across the Atlantic. Until then the focus could be on potential activity in the Caribbean and Gulf of Mexico where seas are already very warm. Alberto might have set the tone for at least the first part of the season but predictions of dry conditions spread to the Caribbean so even that becomes more doubtful.