Over the last two weeks, a high-pressure system has dominated conditions across Trinidad and Tobago, with light winds due to tropical cyclones north and east of the region. The country has now recorded its highest temperatures to date for 2021. While it may feel like a heatwave, technically, the definition has not been met in T&T yet.
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, must last 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.
This Week’s High Temperatures
On September 20th, 2021, even with the isolated showers and thunderstorms across western and southern Trinidad, record high temperatures for 2021 were recorded across parts of Trinidad. Across Trinidad, temperatures ranged between 32°C and 36°C, with urban areas seeing hotter temperatures of up to 38°C. In Tobago, maximum temperatures generally remained between 31°C and 33°C.
At the time, the 34.5°C at Piarco was the highest maximum temperature recorded for 2021. However, this record would be broken 48 hours later.
However, with light winds and relatively high humidity, the temperature you feel outside, or the heat index was much higher. Across Trinidad and Tobago, heat indices were in the danger category, between 40°C and 51°C. This meant that heat cramps and heat exhaustion were likely, with heatstroke probable with continued activity outdoors.
Hot temperatures were recorded across both islands on Wednesday has heat persisted. Across Trinidad, temperatures ranged between 32°C and 35°C, with urban areas seeing hotter temperatures of up to 36°C. In Tobago, maximum temperatures generally remained between 31°C and 33°C.
Across both climate reference stations for Trinidad (Piarco) and Tobago (Crown Point), the hottest temperature for 2021 was recorded at 34.6°C and 32.9°C, respectively.
Across Trinidad and Tobago, heat indices were in the danger category, between 40°C and 51°C. Like Monday, this meant that heat cramps and heat exhaustion were likely, with heatstroke probable with continued activity outdoors.
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.
To date, there has not been a period in Trinidad where temperatures persisted to meet the definition for a short-duration hot spell threshold of a maximum high temperature of 34.0°C (above 33.9°C) for the island.
These hot temperatures have been due to mostly sunny days; light winds all resulting from a weak high-pressure system at the surface to mid-levels of our atmosphere.
Tobago did meet the island’s threshold for a hot spell due to consecutive hot days with maximum high temperatures of 32.0°C and above. These periods occurred between September 14th through September 18th. If today’s (Thursday) maximum high temperature is at or above 32.0°C, then the island would have another short-duration short spell that began on September 20th through today, September 23rd.
While both islands have and continue to experience hot conditions, the country has not met the definition for a hot spell (heatwave). A hot spell alert, watch, or warning has not been issued by the TTMS.
Is this record heat?
Where do these temperatures 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 (1991-2020), stands at 37.8°C recorded on April 20th, 1946 at Wallerfield.
At Piarco International Airport, where the new official records began, the hottest temperature for September was recorded on September 25th, 1990, at 36.5°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, and as relative humidity increases, so does the heat index.
The heat index is generally classified into four categories: caution, extreme caution, dangerous, and extremely dangerous. Generally, across Trinidad and Tobago, through Friday, dangerous heat indices are forecast.
Very High Temperatures Continue, For Now
No tropical waves are forecast to affect the country over the next 5-7 days. However, increased moisture and instability are forecast to move across T&T on Friday and Saturday, bringing variably cloudy skies that could keep temperatures on the “cooler” side (temperatures are still forecast to be in the low thirties).
Then, mostly hot and sunny conditions are forecast to return on Sunday through Wednesday, with high temperatures likely yet again.
In the Trinidad and Tobago Meteorological Service’s (TTMS) Rainfall and Temperature Outlook for Trinidad and Tobago, issued on August 26th, 2021, hotter days are in the forecast.
Usually, the peak of Trinidad and Tobago’s heat season runs from August to October. In most years, September is the hottest month. September through November is likely to be warmer than usual, with both day and night temperatures expected to exceed their averages. There are concerns for an increase in the number of hot days, and short duration hot-spells remain elevated for September and early October (hot days: days with a maximum temperature greater than 33.9°C in Trinidad and greater than 32.0°C in Tobago.
“There is a greater than 70 % chance for daily maximum and night minimum temperatures to be above average, with September and October days and nights likely to be the warmest during the period,” based on the TTMS’s outlook.