Bomb Cyclone to Push Damaging Swells Across the Caribbean

16 01 2020

Dale C.S Destin|

The Caribbean Basin is about to see another round of large and damaging swells reaching its shorelines starting Saturday, from a bomb cyclone. Swells are forecast to exceed 3.5 metres (12 feet) and break at higher heights, as surfs, on coastlines. This is likely to be the biggest swell event since Swellmageddon of March 2018.

Animation of bomb cyclone, east of Canada, with pressure pattern, wind speeds and directions, as forecast by the Global Forecasting System (GFS) Model. Time in UTC

The event will be kicked off by a relatively inconspicuous low-pressure system (LPS), currently over the northeast United States. The LPS will go through explosive development (bombogenesis) over the next 24 hours and become a ginormous and powerful bomb cyclone (extratropical cyclone) over the northwest North Atlantic, with hurricane-force winds.

Although this system will form over 3220 km (2000 miles) away, it will have a significant impact on the region, through its strong winds pushing unusually high waves to our shores. The first set of these swells will reach the Bahamas on Saturday; the northeast Caribbean, including Antigua and Barbuda, on Sunday and the Guianas on Monday. The event will likely last three days from its start time. So, for the northeast Caribbean, its Sunday through Tuesday.

Animation of swells forecast to move across the region from the bomb cyclone, as predicted by the European Centre for Medium-Range Weather Forecasts (ECMWF) wave model (WAM). Time in UTC.

Swells will rise to to in excess of 3.5 metres across most of the Atlantic waters of the islands. There swells will produce even higher surfs or breaking waves. These surfs could be as much as twice the height of the incoming swells, depending on the bathymetry/topography of the near shore seafloor. This is expected to cause beach closures, as swimming conditions will become quite hazardous. Other impacts include:

  • major beach erosion;
  • flooding of some low-lying coastal roads;
  • disruptions to marine recreation and businesses;
  • disruptions to potable water from desalination;
  • damage to coral reefs and
  • Financial losses.

Advisories and warnings will be required for the weekend and or the first half of next week. The event will also be felt along the East Coast of the United States, Canada, Greenland, Iceland, the United Kingdom and Norway. Rowers of the Talisker Whisky Atlantic Challenge will also be negatively impacted, exponentially increasing the challenge of an already very challenging race.

High surf warnings or advisories will be required for coastal areas for much of the Caribbean this weekend and into the middle of next week

The impact on shorelines will not be the same everywhere. Depending on the depth and the natural shelter of the coastal waters, the impact will be different. Moderately sloping, shallow, north and or north-facing shorelines are expected to see the highest swells and surfs.

The bomb cyclone will go from a central pressure of 1004 hectopascals (hpa) (which is the same in millibars) to around 968 hpa in 24 hours and to a minimum of 955 hpa in 48 hours, just east of Newfoundland and Labrador, Canada. This represents an explosive drop of 59 hpa – more than one hpa per hour; thus, meeting the definition of a bomb cyclone – a drop in pressure of an extratropical cyclone of at least 24 hpa in 24 hours or less.

By Saturday, this weather bomb will be packing Category 1, hurricane force winds – 119 to 153 km/h (74 to 95 mph). These are the winds that will, in turn, generate large waves that will traverse the Atlantic and pound the shorelines of the Caribbean, inundating some low-lying coastal areas.

Of course, the hurricane force winds do not even have the remotest of chance of reaching the Islands; however, some of the wind energy, transferred into the seas will reach us in the form of ocean waves – ground swells. As you may know, waves do not transport water; they transport energy, which can de destructive when they break on shorelines.

Animation of wind directions and speeds forecast to impact the region, as predicted by the ECMWF Integrated Forecasting System (IFS) Model. Time in UTC.

Talking about winds, they are expected to surge – getting to the general range of 25 to 45 (16 to 28 mph), across the region again late Saturday and likely continue into Monday. Storm-force gusts to near 65 km/h (40 mph) are expected, especially in showers. Thus, both high wind advisories and small craft warnings are highly possible late Saturday through Monday morning.

Our (Caribbean) weather will also become wet again over the weekend and into midweek. There is a very high chance of occasional brief showers, as the high winds will destabilise the atmosphere via mixing and low-level convergence.

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Another Windy, Rough and Wet Week Ahead

16 12 2019

Dale C. S. Destin|

Rough Seas – Photo by Getty Images

This is a new week, but similar weather is expected to last week’s – windy and wet with rough seas. Winds are expected to surge over the next 24 hours, resulting in the winds becoming fresh to strong by Monday night. This will in turn cause hazardous seas and wet weather across much of the Caribbean Basin, including Antigua and Barbuda.

The winds and seas will be a threat to the life and property of mainly mariners. Some outdoor activities, on land, could also become dangerous.

By late Monday, the winds will rise to the range of 26 to 42 km/h (16 to 26 mph) with stronger gusts . It is expected that the winds will gusts to near storm-force/gale-force – 63 km/h (39 mph), mainly over open waters, exposed coastal areas and elevated terrains.

Given the expected winds, a high wind advisory may be required, particularly for the areas listed above. If a high wind advisory is issued, residents should secure loose and light outdoor items, which can be blown away, and caution should be taken when driving.

As the winds go, so go the seas – as the winds go up, the seas will go up also and become hazardous. Seas (significant wave height – SWH) are forecast to rise to a range of 2 to 3 metres (7-10 feet) with the potential extreme (10% chance) of reaching over 3.5 metres or 12 feet. Notwithstanding, the potential extreme SWH, seas are expected to occasionally reach near 4 metres (13 feet).  

Recall that seas are given as SWH, which is the average height of the highest 1/3 of the waves. Individual waves may be twice the SWH.

Given the expected height of the seas, particularly wind waves, a small craft warning is expected to go into effect for much of the waters of the Eastern Caribbean Monday night through Thursday morning. An advisory is in effect and one will be in effect after the warning.

Recall that a small craft warning generally means that wind speeds of 38 to 61 km/h (24 to 38 mph) and or seas of 9 feet or greater are expected to produce hazardous wave conditions to small crafts. If or when a warning is issued, small craft operators should stay in or near port and safeguard their vessels.

Impacts possible/likely/expected from hazardous seas include the following:

  • Loss of life;
  • injuries;
  • sea search and rescue disruptions;
  • disruptions to sea transportation;
  • scarcity of sea food;
  • damage or loss of boats and fishing equipment;
  • disruptions to marine recreation and businesses
  • and economic losses. 

Other impacts from the high winds, apart from hazardous seas, include:

  • injuries;
  • soil erosion;
  • localized disruptions of businesses;
  • disruption to outdoor and sporting activities;
  • disruption of transportation (air and especially sea) and
  • vehicular accidents and financial losses.

Wind of this strength could make some outdoor activities uncomfortable, if not outright dangerous. High winds can create dangerous fallen or blowing objects.

The strongest winds and the highest and most dangerous seas will take place on Tuesday. The highest seas will take place in the Atlantic waters of the islands.

The strong winds will be due to a very steep pressure gradient. Think of the pressure gradient like a hill and the wind as a car. The steeper the hill the faster the car will roll down the hill and vice versa. On a weather map, the steepest gradient and strongest winds are where the lines of equal pressure (isobars) are closest.

The higher than usual winds will destabilize the atmosphere, resulting in brief passing showers from time to time. Possible rainfall total for the week across the Eastern Caribbean is 25 to 150 mm (1-6 inches). The highest totals are likely across the southern Caribbean.

Last week, similar type weather took place. The area had fresh to strong winds with gusts in excess of 48 km/h (30 mph). The whole of the Eastern Caribbean had wet weather with some areas experiencing rainfall in excess of 150 mm (6 inches).

Seas will subside from warning to advisory levels by Thusday; however, it is unclear as to when seas will return to safe levels – when no warning, advisory or caution is required.

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Storm-Force Winds and Hurricane-Like Seas to Impact Antigua and Barbuda This Weekend

17 12 2016

Dale C. S. Destin |

Significant tightening of the pressure gradient across the area is expected to cause strong winds with frequent gusts to storm force strength or gale force. The seas will respond to the strong winds and become very rough.

Surface chart

Surface Chart for Sunday 8 am, Showing a Tight Pressure Gradient As Evident by the Closeness of the Isobars (pressure lines)

The winds – they will generally be in excess of 18 mph (16 kt) from late Saturday night to Monday afternoon. The winds will peak as high as 30 mph (26 kt) with frequent gusts between 38 and 46 mph (33 and 38 kt) Sunday morning to Monday morning.

High Sustained Winds

Sustained Winds

Wind Gusts

Wind Gusts

The seas –  they will respond to the winds and become very rough, rising to as high as 3.9 metres (13 ft) on Sunday night. Waves will rise above six feet by Saturday morning and remain above this height through midweek. Waves of 2.7 to 3.9 metres (9 to 13 ft) will prevail from Saturday night to Wednesday. Waves are expected to fall off rapidly after Wednesday.

Seas

Seas

The cause – as indicated above, it is the substantial tightening or steepening of the pressure gradient.  This is in response to a very strong surface high pressure system moving from west to east across the Atlantic from the United States.  This will NOT be due to any tropical cyclone (tropical depression, tropical storms or hurricane).

Fundamentally, wind blow as a result of pressure differential (pressure gradient). The greater the pressure between point A and point B (pressure gradient) the stronger the winds.

Where – the strong winds will mostly take place over open waters, exposed eastern coastal areas and elevated areas of Antigua and Barbuda. The seas will be roughest in the Atlantic coastal waters east of the islands, as the winds will be generally easterly. Similar conditions are expected across most of the rest of the Eastern Caribbean. However, Antigua and Barbuda could get the worst of it.

Precautions – The Antigua and Barbuda Meteorological Services have issued warnings for sea-bather and small craft operators. The former should avoid the beaches, especially those on the Atlantic or eastern side of the islands, and the latter should not venture far from port, at least, until Thursday.

A small craft warning generally means that wind speeds in excess of 16 knots is causing or expected to cause hazardous sea conditions to small craft within 24 hours. Inexperience mariners, especially those operating smaller vessels should avoid navigating these conditions.

According to the Beaufort Scale, gale-force winds run from 39 to 54 mph (34 to 47 kt). Operating a vessel in gale conditions requires special expertise and specially equipped vessels. It is highly recommended that mariners without the proper experience seek safe harbour prior to the onset of gale conditions.

The strong winds, especially if frequently gusting to gale force, could also make some outdoor activities very uncomfortable if not hazardous, please be guided accordingly.

We will be keeping a close eye on this developing situation and keep you informed via our social media platform: twitterfacebookinstagramtumblrflickrgoogle+, and youtube.








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