Over the last five days, a high-pressure system has dominated conditions across Trinidad and Tobago, bringing mostly sunny but hot temperatures to both islands, which met the threshold for a short-duration hot spell or heatwave this week.
What is a hot spell?
For a hot spell to be declared in Trinidad and Tobago by the Trinidad and Tobago Meteorological Service (TTMS), a period of hot temperatures, characterized by maximum temperatures of at least 34.0°C (above 33.9°C) in Trinidad and 32.0°C in Tobago, lasting five or more consecutive days. A short-duration hot-spell is three or more consecutive hot days.
It is important to note that for a hot spell, both a normal spell and a short-duration hot spell, the temperature criteria had to be met for both Trinidad and Tobago. We typically don’t see these alerts issued for short duration spells from the TTMS either.
T&T’s Scoarching Temperatures
In Trinidad, data from Piarco are used as the climate reference site by the TTMS while in Tobago, data from Crown Point is used for that island. The temperature data recorded (and forecast) at these sites determine the issuance of a Hot Spell Alert/Watch/Warning.
Since August 25th, 2020, temperatures at Piarco has met the hot spell threshold of (above 33.9°C) 34.0°C for the island, continuing through today (August 29th, 2020). These hot temperatures have been due to mostly sunny days; light winds all resulting from a high-pressure system at the surface to mid-levels of our atmosphere.
Since August 25th, 2020, temperatures at Crown Point has also met the hot spell threshold of 32.0°C for the island, but it only continued through August 27th. This meant that the country (both islands) met the threshold for a hot spell advisory to be issued by the Trinidad and Tobago Meteorological Service. It is unlikely one will be issued as temperatures across Tobago will remain below the threshold level in the coming days. In contrast, hot temperatures are possible across Trinidad for one more day.
Is this record heat?
Where do these temps stand compared to our records? The hottest recorded in Trinidad, based on data from the Global Historical Climatology Network (pre-1980) and the Trinidad and Tobago Meteorological Service (1980-2019) stands at 37.8°C recorded on April 20th, 1946 at Wallerfield.
At Piarco International Airport, where the new official records began, the hottest August temperature occurred on August 23rd, 2017 at a scorching 35.8°C.
The Heat Index
Temps in cities, such as Port of Spain, tend to be much higher than surrounding locations due to a phenomenon called the Urban Heat Island Effect. There are several causes, but the main instigator for this phenomenon tends to be increased dark surfaces such as roads and pavement in cities, which absorb solar radiation more than surrounding areas.
Several persons across the country took to social media to complain about the heat, or more so what outside felt like. This is called the heat index and is a combination of air temperature and relative humidity, determining what the air feels like to a person, i.e., how hot it actually feels.
The heat index is important because of sweating. Your body sweats to cool the skin and maintain a constant, healthy body temperature. This cooling process means that the sweat has to evaporate off the skin to remove heat. However, if the sweat is unable to evaporate, the body isn’t able to regulate temperature.
With high volumes of moisture in the air, also known as high relative humidity, which T&T regularly experience due to its tropical climate, the rate of sweat evaporation decreased. This is because the atmosphere is unable, or has limited potential to hold additional moisture in the atmosphere.
This results in you feeling warmer in humid conditions and cooler in less humid conditions i.e. when relative humidity decreases. As temperature increases, the heat index increases. As relative humidity increases, so does the heat index.
Heat index is generally classified into four categories: caution, extreme caution, dangerous, and extremely dangerous. Generally, across Trinidad and Tobago, we experience heat indices of caution to extreme caution in times of hot days, with isolated areas experiencing dangerous heat indices such as urban areas.
High Temperatures To Continue
In the short term this upcoming week, tropical waves and the ITCZ are forecast to keep temperatures on the cooler side, though hot temperatures are still possible across Trinidad, particularly on Sunday.
In the Trinidad and Tobago Meteorological Service’s (TTMS) Rainfall and Temperature Outlook for Trinidad and Tobago, issued on the 31st, July 2020.
In fact, according to the TTMS, August to October 2020 in Trinidad and Tobago will likely be warmer than usual with potentially risky heat exposure during very hot spells, especially during late August to September.
“There is greater than 75 % chance for maximum day-time and minimum night-time temperatures to be above average, with September days and nights likely to be the warmest during August to October 2020,” based on the TTMS’ outlook.