February to July 2018 Climate Outlooks for Antigua and Barbuda

8 02 2018

Dale C. S. Destin |

Antigua and Barbuda is back in a meteorological drought again. The latest round of climate outlooks suggest that it is unlikely to worsen and could even end in a few months. However, with us entering the heart of the dry season, the prospects of real relief are not good. Beyond the next few months, it is very unclear as to how the rainfall will perform. Meanwhile, temperatures will vary over the upcoming six months.

Rainfall and drought

At least, a meteorological (Met) drought has returned to Antigua and Barbuda as of October 2017. The rainfall totals for our two wettest months – October and November, were below and well below normal respectively. Combined, it is the driest October-November period since 1983 – 34 year ago or in a generation.

Nov2017-Apr2018_Rainfall

Looking forward – the Met drought is likely to remain the same or perhaps come to an end in the next three months or so. Rainfall totals for December and January were near normal and the outlooks for February-April is for above to near normal rainfall.

Although the Met drought may not get any worse, we could still slip into a hydrological drought, if we are not already in one. Catchments are on the decline, as is normal for the dry season, and will unlikely be recharged by the rainfall of the upcoming three months.

Beyond April, rainfall performance is quite uncertain – the signals are all over the place. Hopefully, in a month’s time things will become relatively clear.

The cold phase of El Nino Southern Oscillation (ENSO) – La Nina is evident although an episode cannot yet be declared. La Nina is weak and expected to come to an end around April; hence, having very little impact on rainfall across our area.

If you are in our part of the world – the Caribbean, a moderate or strong La Nina is almost always welcome, particularly in the summer when it has a usual positive impact on rainfall. The opposite – El Nino, has a negative impact. Outside the wet season – July to December, ENSO has little or no effect on our rainfall.

Temperature

Temperatures were generally near normal for the October-December (OND) period. However, the mean minimum temperature was above normal – the second highest since 2002, based on preliminary data.

The warmer than normal mean minimum temperature for OND was due mainly November and December having above normal nighttime low temperatures. This was reflected in the mean maximum temperature, where November and December also experienced warmer than normal daytime high temperatures.

Looking down the road – there is equal chance of the mean and maximum temperatures for the next three months – February to April, being below, near or above normal. However, the minimum temperature is likely to be above to near normal.

For the period May-July, the mean temperature is expected to be above to near normal. There is equal chance of the maximum and minimum being below, near or above normal.

See the following links for the full outlooks: CariCOF Newsletter – summary and outlooks for the region; precipitation outlooks and temperature outlooks.

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Drought Again For Antigua

27 01 2018

Dale C. S. Destin |

None_to_Serious_DroughtAntigua is back in drought again. There are several types of drought and as of three months ending December 2017, rainfall figures indicate that Antigua has slipped into, at least, a meteorological drought.

The drought started October 2017, when less than 40% of the normal total rainfall fell for the month. It was the second driest October since 2000 and the 13th driest on record dating back to 1928. Normally, October is the wettest month of the year – averaging 161.0 mm (6.34 in); however, this year, only 61.2 mm (2.41 in) fell.

November did not fare any better with respect to rainfall, actually, it was worse. November only got around 32% of its normal rainfall. It was the driest November since 1997 – two decades ago.

Normally, November is the second wettest month of the year, averaging (5.97 in) – only (1.95 in) fell last November. Instead of being the second wettest, it was the second driest month of 2017 and the seventh driest November on record dating back to 1928.

December had near normal rainfall – far from enough to have much of a positive effect on the drought. By the end of the three-month period ending December – the rainfall deficit for the said interval was around 49% or (8.00 in). It is the sixth driest October-December period on record. At this deficit, the meteorological drought is deemed to be at serious levels.

OND_SeasonalRainfall

There is no firm end in sight for the current drought – the chance of it ending over the upcoming three months is moderate, at best. It is more likely to remain the same or get worse.

On average, serious meteorological droughts last around 11 months. The chance of a serious drought ending in a hurry i.e. in less than six months is less than 20%.

Already there are signs of catchment drying up. Potworks Dam, the country’s largest catchment, by far, is well below half. In the past, such a drought would be more impactful socioeconomically; however, with the advent of at least two major desalination plants in the past three years, much of the impacts are being masked.

Potworks Dam Jan 16, 2018, Courtesy Karen Corbin

Potworks Dam Jan 16, 2018, Courtesy Karen Corbin – Humane Society

The last meteorological drought – the worse ever on record, came to an end September 2016. The meteorological drought also degenerated into agricultural, hydrological, socioeconomical and ecological droughts, which were quite costly to the economy of Antigua and Barbuda.

Keep following us for more on this developing story and all things weather and climate.

 





Snow in the Sahara Desert – Unbelievable But True!

11 01 2018

Dale C. S. Destin |

sahara-desert-map

A few days ago, snow fell over parts of the Sahara Desert. To many this was unbelievable, especially in this era of fake news and alternative truth. However, it really snowed in the Sahara Desert, and not for the first time. Precipitation (rain, snow, hail, etc.) in deserts are rare but certainly not unheard of.

Algeria - dark green

Location of Algeria – dark green

 

Snow covered dumes in the Sahara Desert. Photo by Geoff

Snow in the Sahara Desert near the town of Ain Sefra, Algeria – 07 Jan 2018. Photo by Geoff Robinson 

It is understandable the disbelieve one would have about the news of snow taking place in the Sahara Desert. After all, it is “only” the hottest desert in the world – consisting of some of the hottest places on Earth. The mean temperature is around 29 °C (84 °F) but can reach as high as 50 °C (122 °F).

What is not well-known is the fact that very cold temperatures do occur in the Sahara Desert. Temperatures, particularly during winter can fall below freezing (below 0 °C or below 32 °F). So, temperatures do become conducive for snow in the Sahara, at times. However, temperature is not sufficient for snow – moisture is needed.

Contrary to popular belief, precipitation does take place in deserts, including the Sahara. Not a lot takes place but they do get precipitation. There is no universal definition for a desert but a good working one is an area receiving less than 250 mm (10 in) of rainfall annually.

In the case of the Sahara, the annual rainfall is less than 100 mm (3.9 in). It rains from December to March and in August. The rains in August are said to be characterized by thunderstorms, which can produce flash floods. And of course, snow falls at times during the winter months, as was the case a few days ago.

It snowed in the same location last year; however, before then it had not snowed in 2012 and 1979 -nearly 40 years ago.

Sahara snow event of 2012 as reported by Algerian TV channel, Central TV

Weird precipitation events are rare for deserts but they do occur:

In January 2013, a NASA satellite observed the Taklimakan Desert, in western China, covered with snow. The Taklimakan Desert temperature range from – 20 to 38 °C (68 °F to 100 °F) and the annual average rainfall is less than 40 mm (1.60 in).

In August 2011, Stephane Guisard of the European Southern Observatory photographed snow in the Atacama Desert. The annual average rainfall is around 1 mm (0.04 in).

A dusting of snow in the Atacama Desert

A dusting of snow in the Atacama Desert. Photograph was taken by Stéphane Guisard on 1 August 2011. 

In March 2015, Flash floods took place in the Atacama Desert – the driest desert in the world and one of the driest places on Earth. The annual average rainfall is around 1 mm (0.04 in). The floods caused two deaths and left 24 persons missing.

Precipitation may be rare for the deserts of the world but far from unprecedented. No only do they get light precipitation but also solid, on occasions.





Windy Weather to Cause More Hazardous Seas and Economic Losses

8 01 2018

Dale C. S. Destin |

Hazardous seas being caused by frequently strong winds – gusting to near gale force at times, will continue to keep most mariners in or near port over the upcoming week – causing further significant economic losses for many.

Seas around Antigua and Barbuda have been rough for most of the year, so far, and are set to remain that way or even worsen over the next seven days, at least. As usual, this type of weather is very disruptive to marine activities and have a negative economic impact, particularly on fisherfolk, those alone the fisheries value-chain and those involve in offshore pleasure cruises and adventures.

Small craft warning remains in effect for hazardous seas around Antigua and Barbuda and will likely remain in place for the rest of the week. Hence, small craft operators, especially inexperienced ones, should avoid navigating in these conditions.

Warnings are also in effect for beach-goers as high surfs are affecting beaches, producing beach erosion and dangerous swimming conditions. Beach-goers should avoid the waters, especially those on the northern and eastern side of the islands. These high surfs are likely to subside to more manageable levels by Tuesday.

High surfs can also cause strong rip currents, which can carry even the strongest swimmers out to sea, and seawater splashing onto low-lying coastal roads, causing damage. Further, high surfs can also knock spectators off exposed rocks and jetties. Breaking waves may also occasionally impact harbours making navigating the harbour channel dangerous.

The wind speed will range between 14 and 22 knots (16 to 25 mph) and at times gusting to near 30 knots (35 mph). The winds will be strongest on Tuesday and Friday and will blow from near east for most of the week.

Wind speed – valid at 6 am, Tue, Jan 9, 2018

Seas will remain hazardous with steep waves ranging between 2 and 3 metres (7 and 10 ft), occasionally reaching near 4 metres (13 ft), mainly in open waters on the eastern or windward side of the islands.

Significant wave height (ft) – valid at 6 am, Tue, Jan 9, 2018

These strong winds not only cause hazardous seas but also cause certain onshore activities to be uncomfortable, if not dangerous. Hence, certain outdoor work will be hampered, if not halted, at times; thus, reducing productivity in other sectors.

The windy conditions and hazardous seas will also be experienced by all the islands of the Eastern Caribbean along with Hispaniola and the Bahamas, particularly the Atlantic coastal waters or the eastern and northern coastal waters.

The strong winds are not due to any storm system but rather because of steep pressure gradients across the area. Recall that winds blow due to pressure differences or pressure gradients, and the greater the gradients the stronger the winds and vice versa.

Also, the strength and position of the ever-present subtropical/Atlantic high-pressure system modulate the steepness of the pressure gradient. The closer and or stronger the subtropical high, the steeper the gradient, the stronger the winds and vice versa.

The subtropical high-pressure system will be stronger than normal for much of the next week; hence, the forecast continuation of strong winds, hazardous seas, disrupted marine activities and economic losses.

Although windy, the weather will be mostly dry with only occasional brief showers likely.

Follow us for all you need to know about this windy weather and all things weather and climate. We can be followed on twitterfacebookinstagramtumblrflickrgoogle+, and youtube.





The 2017 Atlantic Hurricane Season Summary

1 12 2017

Dale C. S. Destin|

The 2017 Atlantic hurricane season came to an end yesterday but will long be remembered for the costliest and one of the most destructive on record. It was also one of the most active hurricane seasons on record, breaking or equalling several records.

Hurricanes Katia (left), Irma (middle) and Jose (right)

Hurricanes Katia (left), Irma (middle) and Jose (right)

The hyperactive season produced 17 named storms, 10 hurricanes, 6 major hurricanes and 223 Accumulated Cyclone Energy (ACE). Overall, it is the seventh most active season on record (based on ACE) dating back to 1851 and the most active since 2005.

AtlanticHUrricaneSeasonSummary

Relative to the normal season of 12 named storms, 6 hurricanes, 3 major hurricanes and 106 ACE, this season had 42% more named storms than normal, 67% more hurricanes than usual, twice the normal number of major hurricanes and over twice the normal amount of ACE.

2017HurricaneSeasonSummaryGraphic

The furious 2017 Atlantic hurricane season left in its wake cataclysmic damage and is now the costliest hurricane season on record with cost amounting to over US$367 billion. The Caribbean contribution to this total is about US$120 billion.

Relative to Antigua and Barbuda

It was the most active hurricane season for Antigua and Barbuda, based on the number and strength of hurricanes passing within 105 nm of the islands. This season marks the first time on record that three major hurricanes passed in such proximity of the country. There have been other times with three or more tropical cyclones but none with three major hurricanes.

For the first three weeks of September, we had a ominous procession of major hurricanes – Irma, Jose and Maria. Irma was the strongest, in terms of sustained winds. The current hurricane scale goes from 1 to 5; however; if there were a 6, Irma would have been a Category 6 – it was super strong with peak sustained winds of 298 km/h (185 mph).

Super-Category 5 Hurricane Irma virtually wiped out Barbuda – damaging or destroying around 90% of buildings. Meanwhile, Antigua got away almost “scot-free” with only storm-force winds causing minimal damage.

Damaged and destroyed properties in Barbuda in the wake of Irma – Sep 6, 2017

Both Antigua and Barbuda dodge the bullets from Jose and Maria. Maria also produced storm-force winds; however, Jose passed without causing any notable winds. Notwithstanding, with Jose passing three days after Irma destroying Barbuda – the whole island had to be evacuated.

The expense to Antigua and Barbuda according to the National Office of Disaster Service (NODS): about US$140 million in damage; around US$20 million in losses and a recovery cost of about US$220 million. Most of the damage took place on Barbuda, where one person died during the passage of Irma.

On average, Antigua and Barbuda gets one named storm passing within 105 nm every other year, one hurricane every three years and a major hurricane every seven years. This is the first year on record we have been affected by Category 5 hurricanes – Irma and Maria.

AntiguaHurricaneSeasonSummary

Why was the season so active?

The season was hyperactive because of warmer than normal sea surface temperatures and very friendly atmospheric conditions – deep moisture levels and below normal vertical wind shear. This was especially so from around mid-August to early September.

The absence of an El Nino and conditions trending toward a La Nina also allowed for a more active season than normal.

Did climate change play a part?

There is no scientific evidence to support the notion that climate change had anything to do with the hyperactive 2017 Atlantic hurricane season or any previous hurricane season.

This is not to say that climate will not eventually have an impact on the hurricane season in the future. According to the Intergovernmental Panel on Climate Change (IPCC), climate change will, in the future, cause an overall decrease in the number of tropical cyclones but an increase in the number of major hurricanes.

Other notable records

Irma is the strongest hurricane on record to occur in the Atlantic Ocean – outside the Caribbean Sea and the Gulf of Mexico.

Maintaining peak intensity for 37 consecutive hours, Irma is the only tropical cyclone on record worldwide to have had winds that strong for so long.

Irma tied with 1935 US Labour Day hurricane for the strongest hurricane to ever make landfall in the Atlantic Basin.

September 2017 is the most active month on record for the Atlantic

Ten hurricanes in a row form during the 2017 Atlantic hurricane season – the most consecutive hurricanes on record.

Click here for more records.

Keep following for more on the just ended hurricane season, tropical cyclones and climate change and all things weather and climate. The next hurricane season starts June 1, 2018 – six months from now, let us all be prepared. Our first forecast for the next season will be issued around April 10.





Tropical Cyclone Size and Climate Change

21 11 2017

Dale C. S. Destin |

This is a continuation of our series – Tropical Cyclones and Climate Change – TCs (tropical depressions, tropical storms, hurricanes). In our previous blog in this series, we looked at Tropical Cyclone Rainfall Rates and Climate Change. In this blog, we will look at whether climate change is having an impact on TC size.

The soon ended 2017 Atlantic hurricane season has produced 17 named storms – five more than the average or 42% more than usual. This is still the most since 2012, when 19 formed. Meanwhile, there have been 10 hurricanes – four more than the average or 67% more than usual. This season remains tied with 2010 for the most hurricanes since 2012. The number of major hurricanes remains unchanged at six – three more than average or twice the usual amount. This is the most major hurricanes since 2005.

Have TCs size increased?

The Intergovernmental Panel on Climate Change (IPCC) is silent on this question. Further, the research on TC size has been quite few and the datasets very limited; however, the current answer is likely no based on available data.

Studies have shown that the size of TCs varies within and across ocean basins. Generally, the size of TCs increases with the increase in latitude or as you move poleward. For the Atlantic, this means that they generally increase in size as you go northward.

Hurricanes Katia (left), Irma (middle) and Jose (right)

Hurricanes Katia (left), Irma (middle) and Jose (right). All three were small hurricanes in terms of the extent of the hurricane and storm winds from their centres.

The initial size of a TC is also indicative of its eventual size when it reaches the maximum intensity. The rate of growth is largest at intensification.

There appears to be a trend toward smaller TCs in most ocean basins that they do form over; however, this trend is not deemed to be significant globally or regionally.

While there appears to be a negative trend in most ocean basins, no significant trend in size have been detected globally or regionally. However, the confidence level of this finding is considered relatively low since the dataset used is relatively short and somewhat subjectively obtained.

Will TCs increase in size in the future?

Although some studies have indicated a decrease in size, it is not clear how size will change in the future with a warming climate. The increase in intensity could be theorized to have both a positive or negative trend on size.

More intense TCs could mean higher pressure gradients due to a tightly ‘rap’ system and no change in central pressure, in that case, the trend in size could be toward smaller systems. On the other hand, if cyclones exhibit lower central pressure, then the trend in size could be toward larger systems. Much more research is needed in this area.

There are lots of talk in the press about TCs becoming larger due to climate change; however, there is no clear evidence to support this claim. There are two main scientific papers that address this matter – one found that the size is decreasing and the other said that the size will increase. However, both papers agree that no change in size has yet occurred due to climate change.

Our next blog in this series will look at the impact, if any, of climate change on tropical cyclone duration.





Tropical Cyclone Rainfall Rates and Climate Change

3 11 2017

Dale C. S. Destin |

This is a continuation of our series – Tropical Cyclones and Climate Change – TCs (tropical depressions, tropical storms, hurricanes). In our previous blog in this series, we looked at Tropical Cyclone Frequency and Climate Change. In this blog, we will look at whether climate change is having an impact on TC rainfall rates.

To date, the 2017 Atlantic hurricane season has produced 16 named storms – four more than the average or 33% more than usual. This is the most since 2012, when 19 formed. Meanwhile, there have been 10 hurricanes – four more than the average or 67% more than usual. This tied with 2010 for the most hurricanes since 2012. Further, there have been six major hurricanes – three more than average or 100% more than usual. This is the most major hurricanes since 2005.

Have TC rainfall rates increased?

According to the Intergovernmental Panel on Climate Change (IPCC), the answer to the above question is no. Recall that the IPCC is the United Nations international body assigned with the task of assessing climate change.

Rainfall totals from Hurricane Maria based on (IMERG) or satellite data

Rainfall totals from Hurricane Maria based on (IMERG) or satellite data

Here is what the IPCC Assessment Report Five (AR5) actually says: “…no broad-scale, detectable long-term changes in tropical cyclone rainfall rates have been reported…”; hence, there can be no credible claim of  TCs producing increased rainfall.

This conclusion by the IPCC is supported by many TC researchers, including Kevin J.S. Walsh et al. and Thomas R. Knutson et al. They all indicate that although the moisture content of the Atmosphere has increased and will continue to do so, as the earth warms, there has been no detectable change in tropical cyclone rainfall rates.

Will TC rainfall rates increase?

To this question, the IPCC says yes! Here are the exact words from the IPCC AR5, “…the increase in rainfall rates associated with tropical cyclones is a consistent feature of the numerical models under greenhouse warming as atmospheric moisture content in the tropics and tropical cyclone moisture convergence is projected to increase.”

According to the IPCC, rainfall rates within 200 km of the centre of TCs are likely to increase by 5 to 20% by the year 2100, due to climate change. This conclusion was also arrived at by many TC researchers including Kevin J.S. Walsh et al. and Thomas R. Knutson et al.

HurricaneIrma_6Sep17

Hurricane Irma rainfall rates – Sep 5-6, 2017. The highest rates are near the centre

The science behind the IPCC conclusion is quite robust. The Clausius-Clapeyron equation indicates that the water holding capacity of the atmosphere increases by around 7% for every degree °C rise in temperature; hence, one can expect increasing water vapour levels in the atmosphere as the earth continues to warm. There is evidence to show that this has happened in terms of rising specific humidity levels; however, studies are yet to detect increased rainfall rates from TCs.

Going forward, TCs will likely take advantage of the increasing moisture levels, in the Atmosphere, to produce higher rainfall rates. However, this is not to say that overall rainfall will increase from these systems as decreasing frequency of TCs could counteract increases. Also, rainfall rates only speak to the amount of rainfall per unit time and not total overall rainfall, which could remain unchanged.

Based on the IPCC and virtually all TC researchers, climate change has not changed TC rainfall rates; the rates remain unchanged. However, they are projected to increase by the year 2100, as TCs will likely extract higher rainfall rates from a moistening Atmosphere, being caused by climate change.

Our next blog in this series will look at the impact, if any, of climate change on tropical cyclone size.








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