Very Hazardous Marine Conditions for Antigua and Barbuda

14 01 2017

Dale C. S. Destin |

 

High Surf

High Surf

The shoreline Antigua and Barbuda and the rest of the northeast Caribbean are getting hammered by high surfs. Additionally, starting today, seas in open waters will become very unfriendly to small craft operators. As a result, the weather authority in Antigua and Barbuda has issued special marine statements on the high surfs and rough seas.

Surfs are building – they are expected to range 8-12 feet (2.4-3.6 m) between today and Monday, affecting mainly northern and eastern coastlines. These high surfs are being generated by a low pressure system located just northeast of the area, which is pushing very large swells to our shores.

There is a high risk of rip currents, especially over the next 24 hours when the surfs are expected to peak. Rip currents are powerful channels of water flowing quickly away from shore, which occur most often at low spots or breaks in the sandbar and in the vicinity of structures such as groins such as jetties and piers.

The winds will become fresh to strongthey will frequently be in excess of 18 mph (16 knots) from today to Wednesday. The winds will peak at around 30 mph (22 knots) with occasional gale-force gusts to the around 39 mph (34 knots) today and Sunday likely.  These winds will primarily take place over open waters, coastal areas on the northern and eastern side of the islands and elevated areas.

windjan142017

windgustsjan142017

The seas will respond to the winds – they will become very rough, rising to as high as 3.6 metres (12 feet) on Saturday night Sunday. Waves will decrease to less than 2.0 metres (6 feet) by Wednesday.

seasjan142017

The cause of the strong winds – this is due to a significantly tight of the pressure gradient (horizontal differential of pressure) across, which will tighten a bit more over the next 24 hours. The relatively tight pressure gradient is in response to a strong high pressure system moving from west to east across the Atlantic from the United States. There are NO tropical cyclone (tropical depression, tropical storm or hurricane) in the area.

Surface Chart

Surface Chart for Saturday 8 am, Showing a Tight Pressure a Tight Gradient as Evident by the Closeness of the Isobar (Pressure Lines)

Precautions – Sea-bathers should avoid the waters, mainly on the northern and eastern sides of the islands until Tuesday. Small craft operators should not venture far from port through Monday.

A high surf warning means that high surf will affect beaches in the advisory area, producing beach erosion and dangerous swimming conditions.

A small craft advisory means that wind speeds of 24-38 mph (21 to 33 kt) and or seas of 7 feet (2.1 m) or greater are expected to produce hazardous wave conditions to small craft. Inexperienced mariners, especially those operating smaller vessels should avoid navigating in these 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.

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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.





Potential Flooding Rainfall to End the Hurricane Season

28 11 2016

Dale C. S. Destin |

Satellite Image - Past 6 hrs Ending 11:45 UTC or 7:45 Local Time

Satellite Image – Past 6 hrs Ending 11:45 UTC or 7:45 Local Time

A surface low pressure system is expected to form near the northeast Caribbean and cause potential flooding rainfall across much of the Eastern Caribbean through Tuesday. Antigua and Barbuda is expected to see peak totals today – Monday.

The system could cause 25 to 100 mm (1-4 in) of rainfall, with locally higher amounts, from the Dominican Republic to Trinidad and Tobago. The epicentre of the rainfall is likely to be just south of Antigua or across the northern Windward Islands where the total could max-out above 100 mm (above 4 in).

North American  Mesoscale Forecast System (Model) Rainfall Accumulations - Nov 27-29, 2016

North American Mesoscale (NAM Model) Forecast System Rainfall Accumulations – Nov 27-29, 2016.

 

Globale Forecast System (GFS) Rainfall Accumulations for the Period Nov 27-29, 2016

Global Forecast System (GFS Model) Rainfall Accumulations for the Period Nov 27-29, 2016

With this type of rainfall, minor flooding is expected and moderate or worse flooding is possible. Hence, flash flood watches and warning may be required for a number of other areas over the next 12 to 36 hours.

This may be a fitting end to a very wet start to November. The month had a near record wet start across the Eastern Caribbean. In Antigua, some areas received upward 200 mm (8 in) during the first 10 days of the month. At the V. C. Bird International Airport, the rainfall stood at 143.5 mm (5.7 in) by November 10 – the third most on record dating back to 1928.

Rainfall Anomalies

Rainfall Anomalies for the Period Nov 1-10, 2016

With this type of rainfall, minor flooding is expected and moderate or worse flooding is possible. Hence, flash flood watches and warning may be required for a number of other areas over the next 12 to 36 hours.

This may be a fitting end to a very wet start to November. The month had a near record wet start across the Eastern Caribbean. In Antigua, some areas received upward 200 mm (8 in) during the first 10 days of the month. At the V. C. Bird International Airport, the rainfall stood at 143.5 mm (5.7 in) by November 10 – the third most on record dating back to 1928.

Recall also, that there were deadly floods and landslides across portions of St. Vincent during the early parts of the month.

The forecast rainfall for Monday is not a foregone conclusion but it is quite possible. If it were to materialized, this November would be one of the wettest on record for much of the Eastern Caribbean. In Antigua, it would be the wettest since Hurricane Lenny’s deluge of 1999 and be among the top 10 wettest Novembers of all time.

After the low, very cool northerly winds are expected to blow across the region. These will likely cause our coolest weather for the season and since February. Night-time temperatures could fall to below 19 °C (66 °F) Monday, Tuesday and Wednesday nights.

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Potentially Record Low October Rainfall for Antigua

29 10 2016

Dale C. S. Destin |

After a very wet September – the wettest since 1995 and the wettest of any month since October 2012, October 2016 is turning out to be a near record dry October across much of Antigua.

top5driestoctobers

Thus far, the rainfall for Antigua and the V. C. Bird International Airport (VCBIA) are 20.6 mm (0.81 in) and 14.3 mm (0.56 in) respectively. These currently rank as driest and third driest respectively on record dating back to 1928.

Interestingly, the anemic rainfall for the month seems largely due to Hurricanes Matthew and Nicole and Invest 99 Disturbance. Matthew brought us some rain toward the end of September. However, once it passed through the Eastern Caribbean it served as a giant sponge in sucking up all of the moisture in the area and only sharing it with those areas it made unwelcome visits on.

Nicole and to a lesser extent Invest 99 did similarly. Since then, wind shear and high pressure systems have made it difficult to rain across our area.

It is not over yet; we could still end up with respectable rainfall for October. In the past, up to 100 mm (4 in) has fallen in the last two days of the month.

La Nina, which is good for rainfall at this time of the year for our region seems on the verge of developing.

Our experimental monthly rainfall forecast, issued for October, indicated that the month was likely to be wetter than normal; this is very unlikely. However, recent weather forecasts from various weather models are optimistic about rainfall for much of next week, some of which are likely for the last day of the October.

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October 2016 to March 2017 Climate Outlooks for Antigua and Barbuda

24 10 2016

Dale C. S. Destin |

The October 2016 to March 2017 climate outlooks are now available for Antigua and Barbuda. Our worst meteorological (Met) drought on record has come to an end; however, other droughts continue. It is unclear what will happen with respect to rainfall over the next six months as there are equal chances of below, near or above normal rainfall for October-December and January-March. Meanwhile, warmer than normal night-time temperatures are likely to continue.

Potworks Dam, Aug242016 (L) v. Sep62016 (R)

Potworks Dam, Aug 24 2016 (L) v. Sep 6 2016 (R). Pictures courtesy Karen Corbin – Humane Society. 

Drought

After over three years, the rainfall for September 2016 has brought the Met and agrometeorological (AgMet) droughts to an end. However, it was not enough to end the hydrological (Hydro) and socioeconomic (SE) droughts, which continue at slight levels or worse. The island-average of 213.4 mm (8.40 in) for September 2016 is the most for a September since 1995. Further, it is the wettest of any month since October 2012.

Drought Meter

Looking forward – below to near normal rainfall is likely for October-March. Meanwhile, there are equal chances of below, near or above normal rainfall for both October-December (OND) and January-March (JFM). Given these and other forecasts, there is a moderate chance of the country going back into Met and AgMet droughts, and the Hydro and SE droughts re-intensifying in the medium to long-term. Drought watches are in effect.

Rainfall Projection for Jul-Dec2016

El Nino Southern Oscillation (ENSO) – El Nino, is happily becoming a distant memory. There is now a 65% chance of a cold phase i.e. La Nina developing over the next three months.

If you are in our part of the world – the Caribbean, a La Nina would be more than welcome. Unlike El Nino, La Nina often brings us more than usual rainfall. Given our severe water crisis of the past three years, a La Nina is being prayed for.

Precipitation and temperature

Year-to-date, the rainfall for Antigua is 1.3 times more than all the rainfall for 2015. Further, it is the wettest January-September since 2013. Notwithstanding, we are still over an inch in the “red” relative to the long-term average of 792.5 mm (31.2 in).

The recent up-tick in rainfall seems to have flattened-out. There is no clear signal as to rainfall for the upcoming seasons: OND, JFM and October-March. The best forecast is trending toward near to below normal rainfall for the next six months.

The projected rainfall for 2016 is 757.3 to 1336.8 mm (29.8 to 52.6 in) or near to below normal. This is at least 182.0 mm (7.0 in) more than last year’s total. There is only a slight chance of above normal rainfall for the year.

For the period October to March, above normal temperature is likely. Further, night-time lows are likely to continue above normal through OND resulting in continued uncomfortable warmer than usual nights.  Relatively cooler nights are likely for JFM.

The hurricane season

The 2016 hurricane season will go down as the first active season since 2012. Thus far, the current Atlantic hurricane season has produced 14 named storms, 6 hurricanes and 3 major hurricanes.

The accumulated energy (ACE) index which matters most, has shot up to 119% of the average of 106 in less than a month from less than 50%. More than half of this ACE is due to the strength and duration of Major Hurricanes Matthew and Nicole.

In terms of numbers, the forecast for the season is on point as it called for around 15 named storms, 7 becoming hurricanes and 3 major hurricanes.

Notwithstanding the end of the season drawing near, we have been seriously impacted by tropical cyclones in November, recall Hurricane Lenny of 1999. Thus, we need to remain fully prepared, as it only takes one hurricane to set our life and community back by decades. Be prudent: stay prepared for the worst and hope for the best!

See the following links for the full outlooks: October 2016, October-December 2016, January 2016-March 2017October 2016-March 2017Drought, 2016 Updated Hurricane Season Forecast.

The next set of outlooks will be available by November 5, 2016.





September 2016 to February 2017 Climate Outlooks for Antigua and Barbuda

29 09 2016

Dale C. S. Destin |

The September 2016 to February 2017 climate outlooks are now available for Antigua and Barbuda. Over the long-term (September-February), above to near normal rainfall is expected. However, in the short-term – September to November (SON), below to near normal rainfall is expected. The droughts are more likely than not to remain as is or end over the short-term. Meanwhile, uncomfortably warm temperatures are expected for the upcoming six months, especially during the short-term.

Drought

August 2016 is the wettest since 2011 and the wettest of any month since November 2014. It was a wetter than normal August with an island-average of 130.3 mm (5.13 in). Notwithstanding, it was not wet enough to end the droughts, which have gone past 38 months.

Looking forward – there is a moderate chance (55%) of the droughts either not getting worse or ending during the period SON. Conversely, there is also a moderate chance of the SON period having below normal rainfall. Notwithstanding, over the long run, above to near normal rainfall is expected. Thus, drought watches are in effect instead of warnings.

jun-nov2016_rainfall

The warm phase of El Nino Southern Oscillation (ENSO) – El Nino, came to an end in May. At which time, the chance of a cold phase i.e. La Nina was in excess of 75%. However, as of this month, the probability of La Nina is at 55% and declining.

If you are in our part of the world – the Caribbean, a La Nina would be more than welcome. Unlike El Nino, La Nina often brings us more than usual rainfall. Hence, given our severe water crisis of the past three years, to not have a La Nina as “promised” would be a great disappointment.

The rains over the past weeks have put a huge dent into the droughts. We are experiencing one of our wettest, if not wettest September in over 20 years. There is optimism that a few of the droughts have ended. More will be said on this, after a full assessment, by the middle of October.

Precipitation and temperature

Year-to-date, Antigua, on average, has had more than twice the amount of rainfall than for the same period last year. Notwithstanding, we are still over three inches in the “red” relative to the long-term average for January-August of 647.7 mm (25.50 in).

This up-tick in rainfall has a reasonable chance of continuing over the long-term: September 2016 to February 2017, there is an 80% probability of above to near normal rainfall. However, the projected rainfall for 2016 is 657 to 1218.5 mm (25.9-48.0 in) or below to near normal.

For the seasons SON (autumn) and DJF (winter), there are equal chances of below, near or above normal mean temperatures. However, over the long-term, mean temperatures are likely to be above normal. Higher than usual night-time low temperatures are likely to continue through November, resulting in continued uncomfortable warmer nights.

The hurricane season

We are passed the peak days of the hurricane season for us and for the season overall. However, we are still very much in the most active period of the hurricane season – August to October. Thus far, the 2016 Atlantic hurricane season has produced, 12 named storms, four hurricanes and one major hurricane.

The 12 named storms are 50% more than the average of 8 to date [September 25]. However, the accumulated energy (ACE) index which matters most, is less than 50% of the average of 106. The relatively low ACE is indicative of the fact that the storms have been generally weak.

The forecast is for a near normal season with around 15 named storms, 7 becoming hurricanes and 3 major hurricanes; this includes those already formed.

Notwithstanding the forecast, we need to be fully prepared, as it only takes one hurricane to set our life and community back by decades. Be prudent: prepare for the worst and hope for the best!

See the following links for the full outlooks: September 2016, September-November 2016, December 2016-February 2017September 2016-February 2017Drought, 2016 Updated Hurricane Season Forecast.

The next set of outlooks will be available by October 5, 2016.





Antigua and Barbuda Battered by Torrential Rains

16 09 2016

Last week Monday, Antigua and Barbuda was battered by torrential rains from a tropical disturbance. This resulted in major flooding in many parts of the country, especially in low-lying and flood-prone areas. We had not seen such downpours in nearly a decade.

Satellte loop of the tropical disturbance

Satellite loop of the tropical disturbance

Many parts of Antigua got more than the average total rainfall for September in less than 24 hours. On average, Antigua got around 139.7 mm (5.5 in) in less than 24 hours, with many areas getting over 180 mm (over 7 in), which is much more than the island-average of 144.0 mm (5.67 in) for September.

RadarRainfallAccumulation-24hrs ending 2amSep62016

Radar rainfall accumulations for the 24 hrs ending 2 a.m. Sep 6, 2016

With the average rainfall total of 139.7 falling on 108 square miles (the size of Antigua), it means that about 8.6 billion imperial gallons (IG) of water fell on Antigua between 2 am, September 5 and 2 am September 6. As a reference, this amount of water could serve the country for three years. It’s also close to 100 times the 90 million IG collected by Potworks Dam.

Clearly, with all this water, it should come as no surprise the we had areas with major flooding. Notwithstanding the negative impacts of the flooding, it was rainfall to make most Antiguans and Barbudans, particularly water resources managers and farmers, smile from ear to ear. It resulted in significant recharging of catchments, many of which were dry or below extraction levels since early last year.

Potworks Dam: left – Aug 24, 2016, right – Sep 6, 2016

Potworks Dam, which was dry for over a year, was filled to around one-eighth, according to the Antigua Public Utilities Authority – APUA (the water authority) . It collected around 90 million IG of water, enough to augment water supplies for the next three to four months. APUA has since indicated an easing of water rationing, at least, for the short-term.

Monday September 5, 2016 was the wettest day for quite a while for many areas of Antigua. At the Airport it was the wettest day since Hurricane Earl’s unwelcome visit in 2010. It was also one of the wettest days since Hurricane Lenny in 1999. Only three other days have been wetter since Lenny – the “father” of all flooding for Antigua.

Although this type of rainfall has been rare for the past 15 years, it does occur fairly frequently at a rate of around once every four to five years, based on rainfall measured at the V. C. Bird International Airport – the home of the Antigua and Barbuda Meteorological Service. In other words, it has about a 20-25% chance of happening each year.

The rains caused major flooding of low-lying and flood-prone areas. This resulted in an unknown number of cars being stalled in flood waters and a number of homes came very close to being flooded. There were minor rock slides reported but damage, if any, is unknown. In the wake of the event, many roads were damage due to erosion.

Flooded road

Flooded road

Flooded road

Flooded yard

The event proved very challenging to forecast. Several days before the event, most models forecast up to five inches of rainfall to occur. However, as we got closer to September 5, the models shifted the rainfall to the south of Antigua. Up to the morning of the event, none of the models surveyed came remotely close to forecast the rainfall that eventually occurred.  

Can we get a repeat of last week Monday?  It is probable but highly unlikely. The chance of getting two such days in a given year is around seven percent. So whereas getting dowsed by such drenching rainfall is not unusual, especially at this time of the year, it is highly unusual for it to happen twice in a year.

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