The Status of Cold Temperature Extremes for Antigua

10 02 2016

Dale C. S. Destin |

Last week we had an extremely cold night (relative to our climate) and a few cool nights which led some persons to ask with “tongue-in-cheek” if we going to have snow. Are cold extremes becoming more or less frequent? What can we expect as our climate changes?

When I was growing up, I remember it was very common place to see our breaths (as mist) in the mornings, due to extremely low temperatures, at this time of the year. It was fun for us as we would pretend to be blowing smoke from our mouths and also blow mist onto the mirrors and then draw or write on them.

The fact is, such low temperature extremes, are decreasing fairly rapidly. So, the cold nights we had last week, are becoming more a thing of the past or a once in a “blue moon” event. 2015 had a record low number of extremely cold nights – 6 or 2% of the number of nights for the year; the next fewest is 2002 with 14 or 4%.

ExtremelyColdNights

Data at the V. C. Bird International Airport (VCBIA), where the Met Office is located, show a significant decline in extremely cold nights, while extremely warn nights are on the increase but not yet considered to be rising significantly.

ExtremelyWarmNights

Extremely cold nights here mean nights with the minimum temperature in the bottom 10-percentile based on the climate period 1971-2000. Extremely warm nights are those with minimum temperature in the top 10-percentile.

This year in particular, nighttime lows are expected to be much higher than normal due mainly to the ongoing El Nino or warmer than usual sea surface temperatures (SSTs) across the equatorial Pacific.

El Nino causes higher than normal surface pressure across the equatorial Atlantic, which acts to weaken the trade winds. Weakened trade winds then translate into warmer than normal SSTs and the air in contact with it; hence the warmer than normal nights.

As our climate changes, cold extremes will continue to decrease and warm extremes are expected to increase. Thus, the drop in temperature to cold extremes will become fewer and the spikes to warm extremes will become more and more common place

Weather extremes are generally undesirable. Cold extremes cost us nothing as it is fairly easy to warm ourselves. On the other hand, warm extremes have negative implications for our health, economy and ecosystem.

So far for the year, there have been fewer than normal extremely cold nights at the VCBIA – one, and more than normal warm nights – nine or 23% of nights to date for 2016.

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Record Low Cool Nights for Antigua

4 02 2016

Dale C. S. Destin |

2015 saw the fewest number of cool nights on record across much of Antigua. At the V. C. Bird International Airport (VCBIA), the number of cool nights – nights with the temperature falling to at least 22 °C (71.6 °F) – was the fewest on record in a series dating back to 1971.

CoolNightsAtOrBelow22C

Never before on record have there been so few days with the temperature falling to at least 22 °C. There were only 4% of days of the year when the temperature fell to 22 °C or lower. For an average year, this number is 11%, almost three times what was observed in 2015.

January and December, on average, are among the months with the highest number of cool nights. However, December had a record low number of cool nights – zero, and January had near record low – four.

Cool nights have been significantly declining over the years. The numbers at VCBIA have dropped from around 15% of days per year in the 1970s to around 7% at present.

This significant decline in cool nights is consistent with what is taking place globally, as our climate changes. According to the IPCC, “It is very likely that the number of cold…nights has decreased and the number of warm…nights has increased on the global scale.”

In general, cool places and times of the day are warming at a faster rate than warm places and times. In our case, nights are warming faster than days. Further, most of the warming being experienced across our area is due mainly to the nights warming at a significant rate.

The mean minimum temperature (mean-min-Temp) for 2015, a proxy for the mean night-time temperature, was at a record high level. The mean-min-temp of 24.5 °C tied with that of 2002 and 2001 for the record lowest.

Apart from cool nights trending downwards most likely due to climate change, the record low rainfall in 2015 contributed a lot to so few days with temperature falling through 22 °C. Evaporation is a cooling process and, when it rains, the water that is subsequently evaporated leads to cooling and reduced temperature. More rain did not fall than fell in 2015; hence, very little evaporative cooling.

On the other hand, the number of warm days – days with the temperature increasing to at least 31 °C (87.8 °F) – was fewer than normal. The year had 19% of days with 31 °C or higher temperature compared to the average of 25%.  These warm days are trending upwards but not significantly, at the moment.

Fewer cool nights have negative implications for our economy and ecosystem. The lack of cool or respite from our virtually year-round oppressive heat will likely hit us in the pocket as we burn more and more energy to keep our bodies from overheating. Heat stress is very costly to our health and well-being and that of our vital flora and fauna.

Follow this space as we bring you more highlights of our weather and climate of 2015. We can be followed on twitterfacebookinstagramtumblrflickrgoogle+, and youtube for education and information on all things weather and climate.

 








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