The Dry Season

The dry season in Trinidad and Tobago is an annual period where lower than average rainfall occurs. Our dry season can start as early as the beginning of January to as late as February and continue until late May or into June.

According to the Trinidad and Tobago Meteorological Service, “The dry season which occurs during January to May is symbolized by a tropical maritime climate that is characterized by moderate to strong low-level winds, warm days and cool nights, with rainfall mostly in the form of showers due to daytime convection. Late May and December are considered transitional periods to the wet and dry seasons, respectively.

Dry Season Declaration

There is no fixed date for the beginning of the dry season. Historically, December into January are the transitional months into a drier climate from the wet season. The Trinidad and Tobago Meteorological Service will officially declare the start of the annual dry season once climatic patterns and chances in atmospheric features are indicative of the region transitioning into a drier state.

Historical dry season start dates based on declarations from the Trinidad and Tobago Meteorological Service
Historical dry season start dates based on declarations from the Trinidad and Tobago Meteorological Service

Once the assessment of criteria necessary for the onset of the dry season has been met and is entrenched, the Trinidad and Tobago Meteorological Service will release a declaration. But what are these criteria?

Characteristics To Declare The Dry Season

  • The Prevalence of Westerly Upper-Level Winds Across the Region. Throughout the year, winds at upper levels of the atmosphere above the Caribbean are from the west. However, during the dry season months, these winds intensify and persist. Conversely, these winds are weaker during the wet season but still present.
  • The North Atlantic Subtropical High-Pressure System. This high-pressure system is a semi-permanent fixture in the North Atlantic, sometimes called the Bermuda-Azores High. During the dry season, this high-pressure system strengthens across the entirety of the North Atlantic, expanding west and southward toward the Caribbean and northern coasts of South America at mid to low levels of the atmosphere.
  • Tighter Pressure Gradient Across the Southern Caribbean. During the year, the typical difference between the pressure at the center of the North Atlantic Subtropical High-Pressure System and Trinidad is between 6 to 8 millibars. However, this difference can become extreme during the dry season, resulting in a significant pressure difference. This increased pressure gradient results in stronger low-level winds, generally from the east-northeast to northeast versus the east, as is seen during the wet season.
  • Reduced Rainfall Rates Due to A General Reduction in Moisture.
  • Stronger Trade Wind Inversion. Yet another consequence of that more robust North Atlantic Subtropical High-Pressure System is sinking air, typical of high-pressure systems. As air rises through the atmosphere, temperatures are supposed to cool. However, as air sinks, it heats up. This creates a layer of warmer than usual air at a certain altitude. This warm layer in the atmosphere develops during the dry season when this high-pressure system is present. An increase in temperature with height is known as a temperature inversion. When it occurs within a trade wind regime, as we have in the Caribbean Region, it is known as a trade wind inversion. Shallow cumulus clouds are seen within trade wind regimes and are capped from becoming taller by a trade wind inversion.
Visualization of a Trade Wind Inversion during the Dry Season.

Dry Season Impacts

It is important to note that the dry season is never without rainfall. Rainfall events, and on uncommon occasions, even thunderstorms, can occur during the dry season, but these events are sporadic but increase during the transition months (December and May).

  • Hot Temperatures. In Trinidad, we classify a hot day as temperatures recorded greater than 34.0°C, while in Tobago, a hot day is classified as 32.0°C. During the dry season, hot days can become frequent. Prolonged hot days can result in heat advisories, which the Trinidad and Tobago Meteorological Service in the past has issued Hot Spell Alerts and Hot Spell Watches. Note that these advisories, based on historical issuance, are only issued if there is the risk of temperatures exceeding 34.0°C during the day and minimum nighttime temperatures above 24.0°C on at least 3-5 days.
  • Heat Stress and Heat Stroke. With hot temperatures, periods of excessive heat can increase the chances of heat stress on persons with heat-sensitive ailments and heat exposed livestock, pets, and other animals. Practice heat safety.
  • Fires. With drier conditions and overall warmer temperatures, surface dryness increases resulting in the browning of weeds, grass, bush, and some forest species and the dry season progresses. This enhances the potential for bush, forest, wild and landfill fires.
  • Reduction in Air Quality. In addition to smoke from pervasive fires, increased surface dryness will also result in increased particulates in the air, aiding in the overall degradation of air quality.
  • Water Scarcity. With a lack of rainfall, there is a reduction in groundwater recharge, surface water flows, and rain-fed water availability. Drier conditions have the potential to affect water reservoirs negatively which can impact the current tourism and carnival seasons.
  • Agricultural Losses. Dry conditions can enhance the chances for agricultural pests and diseases to thrive, in addition to heat and water stress to crops, pastures, and livestock.
  • Increase in Mosquito & Mosquito-Borne Diseases. Drier conditions can increase the need to collect and store water in containers, which can increase breeding areas for mosquitoes.
  • Hazardous Seas. Stronger low-level winds increase the potential for rough seas, affecting marine activities and coastal communities.
  • Drier and warmer conditions tend to favor better quality in some fruits and some outdoor activities;

What Should You Do?

During the dry season, the public is advised to conserve, store, and sustainably manage water. It is also highly recommended for the public to refrain from burning rubbish in grassy or forested areas. The following are tips from the Trinidad and Tobago Meteorological Service.

Have A Water Plan

  • Start conserving water now. Reduce your personal, household, and workspace water usage now.
  • Have a plan to store water safely to avoid the spread of disease from mosquitoes breeding.
  • Have a water backup plan that includes storing water to last 3 -7 days.
  • Find innovative ways such as collecting condensed water from your air conditioner to use for
  • watering plants, washing your cars, and other such activities.
  • Wash less often and wash larger loads at one time.
  • Use water wisely. Turn off taps. Take shorter showers.
  • Lack of water affects sanitation. Have a sanitation plan. Invest in a waterless hand sanitizer.

Have A Heat Plan for The Heat Season (March to May During the Dry Season)

  • Heat on extremely hot days can be harmful to your health. Persons with heart, respiratory, and severe health problems are more at risk during sweltering conditions as heat can make these conditions worse.
  • Have a heat season plan: for babies, elderly and socially isolated persons, young children, and young livestock, all of whom are especially at risk.
  • Plan to keep cool, drink plenty water, take care of others.
  • Be aware of the weather forecasts, specifically forecast temperatures.

Have A Bush Fire and Air Quality Plan

  • Reduce or cut-off lighting outdoor fires.
  • Have a plan to cope with poor air quality due to smoke (remain indoors, keep doors and windows shut, use air conditioners on the recirculation setting so outside air will not be moved inside, keep your windows and vents closed while driving).