Cool Temperatures Overnight Forecast For T&T

A cool and dry airmass settled across Trinidad and Tobago on Sunday, leading to possible cooler-than-normal nighttime temperatures forecast for both islands on Monday morning and possibly Tuesday morning.

What’s causing the cool temperatures?

Over the last 48 hours, an Atlantic High-Pressure system remained in place across the southern Windwards, including Trinidad and Tobago, channeling cooler and drier air toward the region.

The Trinidad and Tobago Meteorological Service did note in their five-day outlook, “As a passing cold front[s] to the near north of the Lesser Antilles continues towards the north-east, a few lines of weak surface convergence are likely to develop across the island chain, along with one or two weak perturbations in the tropical easterly airflow. Cooler air from the northwest and the north continue to encroach on the tropics. There is (sic.) likely to be noticeably cooler air temperatures, especially during the pre-dawn to early morning hours.”

This dry air mass has lower-than-usual relative humidity and little to no cloud cover, with fairly light nighttime winds. Though lines of weak surface convergence are producing some small-scale cloudiness to the east, these clouds are not forecast to significantly affect the radiative cooling process, which may lead to T&T’s cooler nighttime temperatures.

Low temperatures during this time of year are normal, as the Northern Hemisphere experiences winter.

Cool temperatures across Trinidad result from several factors occurring:

• Calm/near-calm winds;
• Little to no cloud coverage;
• Winds originating from the northeast to the north at the lower levels of the atmosphere;
• Low amounts of low-level moisture (water vapor/relative humidity).

The dew point is the atmospheric temperature below which water droplets begin to condense and dew can form. Meteorologists can determine the atmosphere’s moisture content near the surface and estimate the minimum temperature.

A lower dew point means less water vapor in the air. Water vapor can absorb and radiate heat back to the surface. Hence, the lower the water vapor content, the more infrared radiation (i.e., long-wave radiation) can escape from the earth’s surface and cause rapid cooling.

Calm winds and no cloud coverage are due to a persistent subtropical high-pressure system that will begin to dominate the weather for much of January. This system will cause dry air at mid- and upper levels of the atmosphere and inhibit cloud formation.

Lack of cloud coverage also leads to reasonably warm days when temperatures reach 30-32°C.

For vulnerable persons who might be especially susceptible to cooler temperatures, such as babies or people suffering from arthritis, it may be best to layer up to keep warm at night.

Five-Day Temperature Forecast

For tonight (Sunday) through Tuesday, dry conditions are generally expected to persist, with minimal cloud cover expected. This would result in temperatures in the upper teens (18.5°C to 21°C) across Trinidad and lows near or at 22°C across Tobago. Temperatures are forecast to trend cooler in interior areas of Trinidad and Tobago, where winds are lighter, under clear skies, and away from urbanized areas. The official forecast from the Trinidad and Tobago Meteorological Service has nighttime lows at Piarco at 20°C for both Monday and Tuesday.

A shear line north of T&T is forecast to drift southward on Monday, with another shearline developing further south, leading to pockets of moisture that may move across Tobago and the northern portion of Trinidad. As a result, brief cloudy periods and occasional light to moderate showers will mainly cover Tobago and, to a lesser extent, the northern half of Trinidad on Tuesday, mainly interrupting sunny skies. Pockets of dry air are still forecast to be nearby and with winds remaining light, leading to some areas, particularly central and southern Trinidad, seeing a repeat of Monday morning temperatures on Tuesday morning.

By Wednesday, another shearline feature is forecast to develop, with additional weak surface convergence bringing pockets of moisture to Trinidad and Tobago, interspersed with pockets of dry air. As a result, nighttime temperatures aren’t slated to drop sub-20°C, but seasonally cool nighttime temperatures are forecast through the week. These pockets of moisture will also bring brisk isolated showers to the country, particularly from Wednesday into the weekend.

Temperatures are forecast to be far from the record lowest for January. The lowest minimum temperature on record at Piarco is 16.1°C, which occurred on the nights of January 21st and 30th, 1964, followed by 16.4°C on the night of January 28th, 1976.

For Crown Point, Tobago, since 1980, the lowest minimum recorded temperature was 19.0°C recorded on February 4th, 1983, and February 1st, 1992. The lowest minimum temperature for January at Crown Point, Tobago, was on January 2nd, 1984, with a temperature of 19.6°C.

For T&T, the climate reference site for Trinidad is Piarco, where records have been kept since 1946, and Crown Point for Tobago, where records have been kept since 1969.