Rainfall and Temperature Outlook for Trinidad and Tobago, May to July 2021



ISSUED AT: 03:41 PM

Date: Monday 19th of April 2021

Key Messages
  • After a wet March and a transition to a relatively dry April, May is likely to continue the drying trend, across most areas;
  • With ongoing drying favoured to continue in the short-term, the odds are tilted towards drier  than usual conditions with below average rainfall likely for May to July 2021;
  • Drier than usual does not mean the absence of heavy rainfall days or events. Therefore, concerns remain for flash flooding on high risk heavy and prolonged rainfall days, especially during June and July;
  • The percent of average rainfall totals forecasted for the period MJJ, ranges from 78% to 96% of the long-term average;
  • The week of May 10-16 (week 3 ahead) is also likely to be mostly dry. The week of May 17-24 (week 4 ahead) is also likely to be mostly dry;

  • Mostly hotter than usual conditions are expected for May. The chance for very hot days (temperature of at least 34.0oC) and hot spells has increased for May (high confidence);

  • Warmer than average days and nights are likely for the three months MJJ. The chances of being warmer than average are greater than 80% (high confidence);
  • Near average sea surface temperatures (SSTs) in and around Trinidad and Tobago will probably be the main influencer of the local climate in the short term. The Madden Julian Oscillation (MJO) will probably influence suppression of local rainfall during the second half of April.
 

 

 

Likely Impacts

An outlook with increased chances for drier than usual conditions can still have:

  • Heavy rainfall days that are high risk enough to cause severe flooding.
  • Heightened concerns for persons in flood prone areas remain, especially for June and July.

Hotter than average maximum day and night temperatures during May suggests:

  • Heightened concerns for persons with heat-sensitive ailments, vulnerable persons exposed to excessive heat, and heat-stress in livestock and other animals, as well as, in young and transplanted crops.

 


Rainfall and Temperature Outlook for Trinidad and Tobago, May to July 2021



ISSUED AT: 03:41 PM

Date: Monday 19th of April 2021

        Odds Tilt Towards Drier Than Average Condition For May To July 2021

                 But Flash Flood Concerns Remain For High Risk Rain Days

 
Key Messages

 

  • After a wet March and a transition to a relatively dry April, May is likely to continue the drying trend, across most areas;
  • With ongoing drying favoured to continue in the short-term, the odds are tilted towards drier  than usual conditions, with below average rainfall likely for May to July 2021;
  • Drier than usual does not mean the absence of heavy rainfall days or events. Therefore, concerns remain for flash flooding on high risk heavy and prolonged rainfall days, especially during June and July;
  • The percent of average rainfall totals forecasted for the period MJJ, ranges from 78% to 96% of the long-term average;
  • The week of May 10-16 (week 3 ahead) is also likely to be mostly dry. The week of May 17-24 (week 4 ahead) is also likely to be mostly dry;

  • Mostly hotter than usual conditions are expected for May. The chance for very hot days (temperature of at least 34.0oC) and hot spells has increased for May (high confidence);

  • Warmer than average days and nights are likely for the three months MJJ. The chances of being warmer than average are greater than 80% (high confidence);
  • The Madden Julian Oscillation (MJO) is likely to enhance local rainfall during the 1st week of May and suppress it during the 2nd and 3rd week; however near average sea surface temperatures (SSTs) in and around Trinidad and Tobago will probably be the main influencer of the local climate in the short term.

 Likely Impact

An outlook with increased chances for drier than usual conditions can still have:

  • Heavy rainfall days that are high risk enough to cause severe flooding.
  • Heightened concerns for persons in flood prone areas remain, especially for June and July.

Hotter than average maximum day and night temperatures during May suggests:

  • Heightened concerns for persons with heat-sensitive ailments, vulnerable persons exposed to excessive heat, and heat-stress in livestock and other animals, as well as, in young and transplanted crops.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Early  Actions & Preparedness

  • Escalate water conservation programs and awareness messages. Revisit contingency plans to mitigate less than average rainfall;
  • Rain water harvesting should also be encouraged to boost residential water availability;
  • Persons living in flood risk areas should start their flood planning and  preparedness efforts by taking early action in preparing for the upcoming wet season by cleaning drains, canals and guttering. It is not too early to become sand-bag ready.
  • Put  in place the necessary measures to ensure communities are sensitized and start preparedness for the expected increase in rainfall and flooding.
  • Ramp-up de-silting and cleaning of drainage systems, water channels, outlets and river mouths.
  • Initiate contingency planning for transition to, and the upcoming wet season.
 
 

Figure 1: Category of rainfall likely for May to July 2021 (MJJ) 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 MJJ period rainfall totals during the historical period used to produce the outlook.

 

  • The three months from May to July show a moderate chance of drying, which tilt the odds in favour of below average rainfall for both Trinidad and Tobago. The chance of below average is greater than 40%;
  • As such, MJJ 2021 is likely to be less wet than usual. Less than average rains in June and July could still be a large amount of rainfall with periods of prolonged rainfall interspersed by a number of dry days; since both months are usually two of the wettest months for the country;
  • The concern remains for flash flooding during heavy and prolonged rainfall events during the period;
  • Much of Trinidad and Tobago typically receives a high amount of rainfall (in excess of 600 mm on average in Trinidad and 400mm in Tobago) during MJJ; meaning, for below average rainfall to occur,  a large shortfall in rainfall amount (as much as 150 mm on average in Trinidad and 100 mm in Tobago) is needed.

 Figure 2:  Percentage of average rainfall totals likely for May to July 2021.

  • The percentage of average rainfall likely for May to July ranges between 78 % and 96% of the long term average (LTA) in Trinidad but between 88% and 94% of the LTA in Tobago;
  • The start of the wet season is likely to be delayed.

Figure 3: The map shows the chance for extremely dry conditions over the three months, ending July 2021. Extreme refers to the lowest 10% of May to July accumulated rainfall totals in the historical record.

  • There is a moderate chance for extreme low rainfall totals (i.e. rainfall totals within the lowest 10% of all totals in the historical record for MJJ);
  • The chance for May to July 2021 to be within the lowest 10% of all MJJ rainfall totals on record is between 12-29%. Still relatively low but very probable;
  • The outlook indicates a 30-40% chance for at least three 7-day dry spells during May to July 2021.
 

Figure 4: Possible accumulated rainfall totals with the highest chance of occurring during May to July 2021.

  • There is a 41-55% chance that the largest accumulated totals for MJJ 2021 are likely to range between 640mm and 798mm;
  • Areas in eastern Trinidad, stretching from Biche to Valencia are expected to receive the largest rainfall totals;

  • The least rainfall totals are expected in Tobago and areas in the immediate vicinity of the entire west coast of Trinidad. Possible accumulated totals for these areas range between 384mm and 554mm;
  • Fewer wet days than usual possible during MJJ.

 

Figure 5: Possible rainfall totals with the highest chance of occurring during May 2021.

  • A drier than average pattern is expected to continue for most of May 2021, with rainfall totals likely to be in the below average;
  • May is likely to be the driest month within the MJJ period with rainfall totals likely to range between 47.0 mm and 140.0 mm in Trinidad and between 47.0 mm and 95.0 mm in Tobago;
  • The chance for these totals to occur is greater than 45%, which is larger than the chance for above average or near average totals.

Figure 6: Category of rainfall most likely for August to October (AS)) 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 ASO period rainfall totals during the historical period used to produce the outlook.

  • The early outlook for August to October 2021 (ASO) favours a transition to a wetting trend with above-normal rainfall forecasted for both islands;
  • The chance for this to occur is greater than 46% in most areas.

Temperature Outlook:

  • May is usually the end of the first peak of the local heat season. May 2021 is forecasted to be just as warm as usual, with warmer than average days and night;
  • May to July day and nighttime temperatures are forecasted to be warmer than average over all of the country, but are expected to be warmer in Trinidad than in Tobago, and warmest in the cities and urban areas;
  • The chance for warmer than average maximum day and minimum night temperatures is 80% for both  islands;
  • There are increased chances for hot days (days with maximum temperatures reaching or exceeding 34.0oC in Trinidad and 33.0oC in Tobago) in May, particularly during the first fortnight.

Figure 7: The map shows the colour-coded category (below-normal, above-normal, and near-normal) of maximum and maximum temperatures that is most likely to occur across Trinidad and Tobago for the MJJ 2021.  The colour-coded bar-graph with the numbers to the right gives the likelihood for each forecast category to occur.

Likely Implications

  • Drier than usual conditions for the forecasts period can still have sufficient heavy rainfall days that are high risk enough to cause severe flooding. Flash flood risk remains elevated in known flood prone areas;
  • Less than average rainfall tend to lead to reduced water reservoir levels and decreased surface water flows;
  • The potential for high levels of surface water evaporation is enhanced for May, due to the combined effect of hotter than usual conditions and less than average rainfall;
  • Drier than average conditions and warmer than average temperatures tend to favour better quality in some fruits;
  • Increased rainfall, mixed with warm and humid conditions, tend to promote rapid multiplication of some agricultural pests, diseases and fungal growth;
  • Increased rainfall raises the chance for water ponding, which increases the potential for mosquitoes to breed. This may lead to increased chances for spikes in vector borne illnesses;

  • Periods of excessive heat can amplify existing health conditions in for persons with heat-sensitive ailments, worsen chronic health conditions in others and increase heat-stress for heat-exposed vulnerable persons;

  • Increased heat may increase the need to access cooling, which requires energy;

  • Hot days and spells can cause heat stress in livestock and wilting in newly transplanted and younger crops;

  • Warmer than usual temperatures can lead to warmer than usual water-temperatures, which are particularly important for the health of aquaponic fishes  and plants;

  • Water temperatures much warmer than 30.0oC can affect warm-water fishes such as tilapia;

  • Taking action ahead of time to support crop production and livestock health could prevent agriculture production loses.

 

Sectorial Early Actions  and Preparedness That Can Be Taken To Reduce Possible Impacts

 Water and Energy sector

  • Escalate water conservation programs and awareness messages. Revisit contingency plans to mitigate less than average rainfall;
  • Rain water harvesting should also be encouraged to boost residential water availability;
  • Ramp-up de-silting of major rivers and reservoirs, now;
  • Remove dry branches and tree-overhang near electrical wires, especially in landslip prone areas.

General Public

  • Take measures to lessen the impacts of the expected heavy rainfall days and reduced rainfall;
  • Persons living in flood prone areas should start their flood planning and preparedness efforts;
  • Citizens should start early preparedness actions for the expected increase in rainfall during the upcoming wet season by cleaning drains, canals and guttering. Become sand-bag ready.

Disaster Risk Management Sector

  • Put in place the necessary measures to ensure communities are sensitized;
  • Start preparedness for the expected increase in rainfall and the associated negative impacts;
  • Review contingency plans and early warning information dissemination channels.

Drainage

  • Ramp-up de-silting and cleaning of drainage systems, water channels, outlets and river-mouths.

Agriculture & Food Security Sector

  • Take advantage of the expected increase in rainfall to maximize crop management;
  • Raise awareness on agriculture pest and disease control measures;
  • Initiate contingency planning for transition to the upcoming wet season and less than usual rains.
  • Initiate contingency planning for excessive heat;
  • Increase disease surveillance for agriculture diseases that pose a threat.

Waste Management Sector

  • Review contingency plans, operational practices and controls such as diverting local rainfall water-flows away from waste heaps, typically used for mitigating and preventing leachate and contamination of ground surface water.

Health Sector

  • Revisit contingency plans to manage spikes in vector-borne and excessive heat ailments.
Be vigilant and visit the Met. Service website at www.metoffice.gov.tt regularly and follow us on social media to keep up to date with local weather changes. Download our mobile app on Google Play Store or Apple iStore.

Climatic Influencers and Context of the Outlook

  • Sea surface temperatures (SSTs) in waters surrounding Trinidad and Tobago are currently near average to cooler than average. Outputs from climate models indicate near average SSTs are likely during MJJ;
  • La Niña continues to decline and is set to transition El Niño–Southern Oscillation (ENSO)-neutral during May. The outlook indicates (ENSO)-neutral is likely throughout MJJ;
  • ENSO-neutral on the cool-side tends to have little to no influence on local rainfall;
  • The North Atlantic Oscillation (NAO) has been in its negative phase during April and is forecasted to remain in negative phase during May;
  • The Madden Julian Oscillation (MJO) is expected to track across the western hemisphere in the next two weeks and is likely to enhance local rainfall during the 1st week of May and suppress it during the 2nd and 3rd week.

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.