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Wetter than average conditions most likely for December and the 2021 Dry-Season
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Key Messages
- Despite this, there is likely to be many sunny days with typical dry season weather, including visitation of typical dust haze events;
- The country is likely to get about 90 dry-days during the season, which is less than the average of 109 dry-days ( a dry-day is a day with less than 1.0 mm of rainfall);
- The country usually receives 3 to 8, 7-day dry spells and 1 to 5, 10-day dry spells in the dry season. For 2021, there is a 65% probability for one (1) to four (4), 7-day dry spells and one (1) to three (3), 10-day dry spells;
- A number of hot days, leading to short-duration hot-spells are likely during April & May;
- Few nights during January and February are likely to be relatively cold with minimum temperatures falling below 20.0oC;
- Existing La Niña conditions are likely to last into the 2021 local dry season and this influences the wetter than usual local conditions, significantly.
Likely Impact
- Above-normal rainfall would maintain relatively high river and surface-water flow levels and soil moisture content during December;
- Riverine and flash flood potential remains elevated during December and early January, particularly for known flood-prone areas and new/recent flood risk areas;
- Elevated risk is maintained for landslips and landslides in hilly areas during prolonged rainfall periods and heavy rainfall days; Continuation of favourable rains for water management & agriculture can be expected during the period;
- Above normal rainfall totals during the dry season are often not significantly large rainfall totals;
- Enhanced rainfall or a bit extra rainfall will benefit the farming community, but can also elevate the risk of dry-season flooding for some flood prone areas, including farm fields;
- Wetter than usual conditions are likely to subdue, but not eliminate bush-fire potential early in the season, hence the risk of reduced air-quality still exist;
- Wetter than usual condition can also lead to more water ponding, which can promote mosquito breeding and elevate the risk of dengue incidences;
- Elevated daytime and nighttime temperatures during March to May can negatively impact heat- related ailments and livestock;
- Excessive heat later in the season is likely to increase water evaporation rates.
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Early Actions & Preparedness
- Closely monitor the Trinidad and Tobago Meteorological Service weather forecasts;
- Continue water conservation programs and awareness messages;
- Revisit dry season contingency plans and upgrade based on historical extremes and not historical averages;
- Ramp up contingency plans to mitigate the effect of above average temperatures and evaporation rates;
- Continue de-silting and cleaning drainage systems, water channels, outlets and river mouths;
Figure 1: The category of rainfall most likely for the 2021 Dry Season (January to May) with the highest forecast chance of occurrence, expressed as probabilities, is coloured on the map. The most likely category for above-normal, near-normal and below-normal is shown in blue, green and brown shadings respectively. The baseline period is 1981-2010. Normal is defined by rainfall totals observed in middle one-third of Dry season during the baseline period.
- The 2021 Dry Season outlook shows moderately enhanced chances for wetter than usual conditions with above normal rainfall totals likely;
- The season is still likely to produce many sunny days with typical dry season weather;
- On average the country receives 109 dry days (days with less than 1 mm of rainfall) in the dry season. The country is likely to get less than the average number of dry days during the 2021 dry season with a 60% probability for close to 90 dry days;
- Typically, the country receives 3 to 8, 7-day dry spells and 1 to 5, 10-day dry spells in the dry season. For 2021 there is a 65% probability for 1-4, 7-day dry spells and 1-3, 10-day dry spells.
Figure 2: Possible accumulated rainfall totals with the highest chance of occurring during 2021 Dry Season (January to May).
- Above average rainfall in the dry season, often does not mean substantial rainfall;
- Usually, the country receives 412.0 mm of rainfall during the dry season with Trinidad receiving on average 434.0 mm and Tobago 344.0 mm;
- Possible accumulated rainfall totals for the 2021 Dry Season range between 435-920 mm in Trinidad and between 460-660 mm in Tobago;
- Typically March is driest month in the dry season; however, April 2021 is likely to be the driest month in the dry season;
- Expect an increase in dust-haze days as the season progresses with March to May likely to produce the largest number of dust-haze days.
Figure 3: Category of rainfall likely for December 2020 to February 2021 (DJF) with the highest chance of occurrence expressed as probabilities and colour coded on the map. Blues indicate that it is more likely for above normal rainfall to occur than for below normal or near normal. Browns indicate it is more likely for below normal rainfall, while greens indicate it is more likely for near normal rainfall. Normal is defined by the rainfall that was observed in middle one-third of the DJF period rainfall totals during the historical period used to produce the outlook.
- The December 2020 to February 2021 (DJF) rainfall outlook shows there are much enhanced chances for wetter than usual conditions across the country, with above-normal rainfall as the most likely category (high confidence);
- The percent chance for above-normal seasonal rainfall totals is greater than 55% in most areas;
- There is an 80 % chance for at least one 7-day wet spell during DJF (i.e. seven consecutive days with rainfall greater than 1.0 mm).
Figure 4: Category of rainfall most likely for January to March (JFM) 2021 with the highest chance of occurrence expressed as probabilities and colour coded on the map. Blues indicate that it is more likely for above normal rainfall to occur than for below normal or near normal. Browns indicate it is more likely for below normal rainfall, while greens indicate it is more likely for near normal rainfall. Normal is defined by the rainfall that was observed in middle one-third of the JFM period rainfall totals during the historical period used to produce the outlook.
- Strongly enhanced chances for the first half of the dry season (January to March) to be wetter than usual with greater that 60% in most areas for above normal accumulated rainfall totals to occur.
Figure 5: Category of rainfall most likely for March to May 2021 (MAM) with the highest chance of occurrence expressed as probabilities and colour coded on the map. Blues indicate that it is more likely for above normal rainfall to occur than for below normal or near normal. Browns indicate it is more likely for below normal rainfall; while greens indicate it is more likely for near normal rainfall. Normal is defined by the rainfall that was observed in middle one-third of the MAM period rainfall totals during the historical period used to produce the outlook.
- Moderately enhanced chances exist for a wetter than usual overlapping second half of the dry season March to May 2021, with above normal accumulated rainfall totals likely.
2021 Dry Season (January to May) Temperature Outlook
- Both day and night-time temperatures are likely to be warmer than average for most of Trinidad and Tobago during December and the 2021 dry season;
- The chance for warmer than average maximum and minimum temperatures is 55% for both islands;
- Although warmer than average conditions are forecast, high temperatures are not likely to be very uncomfortable during December, January and February;
- March to May which is typically the start of the local heat season is likely to produce one or two short-duration hot spells, but most likely during April and May;
- On one or two cloud-free nights, minimum temperatures are likely to cool below 20.0oC during late December, January and February.
Figure 6: The map shows the percent chance of the colour-coded category (below-normal, above-normal, or near-normal) of maximum and minimum temperatures that is most likely to occur across Trinidad and Tobago for December 2020 and the 2021 Dry Season. The colour-coded bar-graph with the numbers to the right gives the probability for each forecast category to occur.
Likely Implications
- High potential for flash and riverine flooding remains for December and early January;
- The risk of landslides remain high along the North Coast Road, Naparima-Mayaro Road and other known land-slippage areas of Trinidad and along the North-side and Windward Roads in Tobago, particularly during December;
- Above normal rainfall totals during the dry season are often not large rainfall totals;
- Above normal rainfall totals are likely to slow decreases in water levels, river and stream flows;
- Wetter than usual conditions will assist with farmers crop water management but can also promote agricultural pests and diseases growth;
- Excessively wet days can also elevate flood risk during the dry-season for some flood prone areas, including farm fields;
- Wetter than usual conditions are likely to subdue ideal weather conditions for bush-fires to thrive during the season but will not eliminate the risk of bush, forecast and land-fill fires occurring;
- Bush, forest and land-fill fires along with dust haze has the potential to reduce air quality and negatively affect persons with existing respiratory ailments;
- Wetter than usual conditions tend to cause more water to pond, which can promote mosquito breeding and elevate the risk of dengue incidences;
- Elevated daytime and nighttime temperatures during March to May can negatively impact heat related ailments and livestock;
- Excessive heat later in the season is likely to increase water evaporation rates.
Early Actions & Preparedness
Water and Energy sector
- Continue water conservation programs and awareness messages;
- Revisit dry season contingency plans and upgrade based on historical extremes and not historical averages.
- Ramp up contingency plans to mitigate the effect of above average temperatures and evaporation rates.
General Public
- Persons living in flood risk areas should continue their flood planning and preparedness;
- Avoid parking cars where they are likely to be hit by falling trees or power lines;
- Maintain sand-bag readiness;
- Conserve, store and manage water safely and adequately. Take measures to lessen the impacts of dry season conditions. Be dry season ready. Stock up on water.
Disaster Risk Management Sector
- Sensitize vulnerable communities on the forecast, its negative impacts and actions to be taken;
- Review dry season contingency plans and early warning information dissemination channels.
Drainage
- Continue de-silting and cleaning drainage systems, water channels, outlets and river mouths.
Waste Management Sector
- Ramp-up contingency plans to mitigate the occurrence of landfill fires.
Health Sector
- Revisit contingency plans to manage spikes in vector-borne diseases, dust/smoke-related respiratory ailments and heat-sensitive conditions.
Agriculture & Food Security Sector
- Raise awareness on agriculture pest, disease and heat- control measures and bushfire risks;
- Initiate contingency planning for possible dry season farm flooding.
Be vigilant and visit the Met. Service website at www.metoffice.gov.tt regularly to keep up to date with local weather changes and follow us on social media.
Climatic Influencers and Context of the Outlook
- Sea surface temperatures (SSTs) in waters surrounding Trinidad and Tobago are currently near average to slightly warmer than average. Multiple climate models suggest most of the Dry Season is likely to maintain warmer than average SSTs in waters surrounding Trinidad and Tobago.
- Warmer than average SSTs in waters east of Trinidad and Tobago and migrating mid-latitude systems into tropical areas are likely to be the primary driver of Trinidad and Tobago’s climate over the dry season.
- La Niña conditions continue in the tropical Pacific Ocean with an 85% chance to persist into the first half of the 2021 local dry season. The majority of models suggest SSTs in the area used to monitor La Niña will continue to cool until at least February 2021. Based on this, it is likely that at its peak, the La Niña will be moderate to strong.
- Historically, La Niña usually increases instability, reduces wind and wind-shear in the region and enhances dry season rainfall in both Trinidad and Tobago.
- After being in its positive phase during November, the North Atlantic Oscillation (NAO) is forecast to maintain its positive phase for the first two weeks of December then transition to negative-phase and remain in negative phase during January and February. A negative NAO tends to promote weaker trade winds, which can lead to the warming of SSTs in waters surrounding Trinidad and Tobago in the short term.
- The Madden Julian Oscillation (MJO) is the main climate feature which directly influences fluctuation in tropical weather on weekly to monthly timescales. The MJO is not likely to significantly influence local rainfall during January 2021.
The rainfall and temperature outlook is based on statistical and dynamical seasonal climate models outputs and known seasonal climate influencers. The outlook is in reasonable agreement with several of the global climate models. Multiple climate influencers appear to be at play, but La Niña is likely to dominate.
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