Wetter Than Usual End to the 2021 Wet Season Likely for Trinidad and Tobago
Flood Potential Remains Elevated
- Wetter than usual conditions are expected for October to December with rainfall totals likely to be above normal.
- Unusually wet conditions are likely for October with the likelihood for above-normal rainfall higher in October than for November and December.
- October is likely to be the wettest month of the period when the ITCZ is likely to dominate.
- The Extended Range forecast for weeks 3 and 4 ahead shows that the week of October 8th to 14th is likely to be very wet while the week of October 15th to 21st is likely to be wet.
- Much of the country shows a greater than 50% chance for OND rainfall totals above 700 mm.
- October and November are usually the two most flood-prone months in Trinidad and Tobago. Unsettled conditions during October are likely to produce sufficient heavy rainfall days to maintain elevated concerns for flooding and landslides during the month.
- There is sufficient information indicating that flood risk is present and remain elevated within the country;
- The 3-month period from January to March 2022 is likely to get below-normal rainfall totals.
- Maximum and minimum temperatures are likely to be warmer than average.
- One or two hot days (maximum temperatures ≥34.0oC) are likely during early October.
- Cities and urban areas are likely to get the most intense heat.
- The rainfall influencing phase of the Madden Julian Oscillation (MJO) is a key factor that is likely to favourably enhance local rainfall totals during the 2nd and 3rd weeks of October.
- The OND outlook takes into consideration possible developing La Nina conditions in the equatorial Pacific Ocean as a key factor.
An outlook with increased chances for wetter than usual conditions suggest:
- Expected rainfall and ongoing soil wetness enhance the risks for rainfall-induced landslides.
- Heightened concerns exist for persons in occasionally flooded and flood prone areas.
- Elevated risks for heavy rainfall days and prolonged wet periods.
Early Actions & Preparedness
- Strengthen community coordination with disaster management personnel;
- Persons living in flood risk areas should stregnthen their flood planning and preparedness efforts;
- Take every action to maintain emergency supplies that can allow for sheltering in place for seven days;
- Purchase emergency supplies and pack a grab and go-bag with clothes and essentials and have these on standby;
- Get acquainted with your flood prone areas, shelter locations and become sand-bag ready;
- Develop an evacuation plan that outlines the safety of family members and pets;
- Update contact information for the local disaster officials and other emergency services.
Figure 1: Category of rainfall likely for October to December 2021 (OND) 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 OND period rainfall totals during the historical period used to produce the outlook.
- Rainfall for October to December is likely to be above-normal all of Trinidad and Tobago with the chance of exceed normal totals greater than 40% over large areas;
- Model outputs used for guidance maintains previous months elevated probabilities for wetter than usual conditions for OND with increased chance for unusually wet periods and wet days;
- October rainfall totals have increased and OND accumulated rainfall totals are usually among the highest totals. Therefore, above normal rainfall for OND are likely to be substantial amounts of rainfall;
- Given grounds are reasonably soaked and water table levels relatively high, concerns increase and remain elevated for flooding during heavy and prolonged rainfall events.
Figure 2: Percentage of average rainfall totals likely for October to December 2021.
- All of Trinidad and Tobago show the percent of average rainfall is likely to be greater than 100% and supports the probability of wetter than average conditions;
- Percent of average rainfall totals are likely to range from 103% to 126% of average or 3% to 26% more rainfall than average.
Figure 3: The map shows the chance for extremely dry conditions over the three months, ending December 2021. Extreme refers to the lowest 10% of September to November accumulated rainfall totals in the historical record.
- The percent chance for October to December rainfall totals to be among the driest 10% of OND on record is low to moderate.
Figure 4: Possible accumulated rainfall totals with the highest chance of occurring during October to December 2021.
- Much of Trinidad shows a greater than 50% chance of rainfall totals above 700 mm during OND.
- Possible accumulated rainfall totals for OND range between 530 mm and 1100 mm;
- Areas long the foothills of the northern range in north-eastern Trinidad and the eastern part of the east-west corridor are likely to be the wettest areas, where accumulated rainfall totals are likely to reach and exceed 900 mm with totals as high as 1100 mm possible;
- Areas in Tobago’s southwest near Crown Point, Low Lands and Buccoo can expect rainfall totals around 530 mm, while areas in the northeast, near Mount Saint George and Kings Bay and north-side near Moriah and Castara are likely to get totals close to 900 mm.
Figure 5: Possible rainfall totals with the highest chance of occurring during October 2021.
- October is likely to be unusually wet with a wet regime and associated unsettled conditions set to dominate and drive above-normal rainfall totals across most of the country;
- The chance for October rainfall to be above-normal is greater than 45%;
- Expect monthly totals from near 140 mm to 450 mm in Trinidad and between 115 mm and 325 mm in Tobago;
- The Extended Range forecast indicates that the week of October 8th to 14th and 15th to 21st are likely to be wet, with October 8th to 14th likely to be the wettest.
Figure 6: Category of rainfall most likely for January to March 2022 (JFM) 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.
- It is likely that the 3-month period January to March 2022 will be drier than usual with below normal totals as the most favourable category to occur.
- October to December temperature outlook favours above-normal monthly mean temperatures, with warmer than average conditions expected;
- Both day maximum and night minimum are expected to be warmer than average with greater than 62% chance for this to occur;
- October temperatures are likely to be warmer than average with the greatest percent chance occurring over cities and urban areas;
- October usually brings the local heat season to a close. There is a slight chance for maximum temperatures to climb near or above 34.0oC during the month, but this is more likely during the first week of the month;
- Cities, urban and developed areas have the highest chance for warmer than normal temperatures and experience the most intense heat on hot days;
- The risks for hot days and hot spells are highest for early October.
Figure 9: 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 October to December 2021. The colour-coded bar-graph with the numbers to the right gives the likelihood for each forecast category to occur.
- Above-normal rainfall for OND usually produce a number of moderate and heavy rainfall days that are high risk enough to cause severe flooding. Flash flood risk remains elevated in occasional and well-known flood prone areas;
- Localized moderate to heavy rainfall days on already soaked soils could trigger flash-flooding in high-risk/flood-prone areas and floods and landslides within watersheds with narrow valleys and steep hill-sides;
- Expect recharge rates, surface water flows and river levels to remain high;
- Expect increased turbidity and degraded water quality on heavy rainfall days;
- More reliable rains for agriculture but the excess rainfall can lead to water logging and flooding of agricultural fields;
- Increased rainfall, mixed with warm and humid conditions will likely promote rapid multiplication of some agricultural pests, diseases and fungal growth;
- Increased rainfall could lead to reduced traffic flows, disruptions in localized travel, and longer travelling times, which may require earlier commute start-times;
- Increased rainfall will increase surface water ponding and can promote mosquito breeding, which can lead to higher risks for spikes in vector-borne diseases;
- Higher than usual and extreme temperatures can lead to relatively excessive heat for Trinidad and Tobago which can amplify existing health conditions in vulnerable persons and worsen chronic health conditions in others during the rest of the local heat season;
- 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;
- Water-logged agricultural fields can reduce soil oxygen and increase the loss of nitrogen and other important nutrients, which can negatively affect fruit and crop quality and yields;
- Warmer than usual temperatures can lead to warmer than usual water-temperatures, which are particularly important for the health of aquaponics fishes and plants and hydroponic plants;
- Water temperatures much warmer than 30.0oC can affect warm-water fishes such as tilapia.
Sectorial Early Actions and Preparedness That Can Be Taken To Reduce Possible Impacts
- Persons living in flood risk areas should take every action now to strengthen flood preparedness and response plans, while paying greater attention to the daily weather forecasts.
- Maintain emergency supplies to shelter in place for seven days and a grab and go-bag with clothes, medicines and essentials and have these on standby;
- Be sand-bag ready and get acquainted with the nearest and alternative shelter locations;
- Develop an evacuation plan that outlines the safety of family members and pets;
- Update contact information for the local disaster officials and other emergency services
Disaster Risk Management Sector
- Continue sensitization and awareness building in vulnerable communities;
- Ramp-up preparedness , restock response consumables and heighten awareness messages about the expected rainfall and the associated negative impacts;
- Test and re-check emergency check-lists, contingency plans and warning dissemination channels.
Water and Energy sector
- Update flood action plans and continue water conservation awareness messaging;
- Continue to remove dry branches/tree-overhang near electrical power wires
Drainage & Infrastructure
- Continue de-silting and cleaning of drainage systems, water channels, outlets and river mouths;
- Visit and pre-check areas known for rock fall and revisit contingency plans for landslides and flooding for areas so prone.
Agriculture & Food Security Sector
- Raise awareness on agriculture pest and disease control measures. Revisit flood action plans.
Waste Management Sector
- Review contingency plans and operational practices (such as diverting rainfall water-flows away from waste heaps) used for mitigating/preventing leachate and contamination of ground/surface water.
- Revisit contingency plans to manage spikes in vector-borne and excessive heat ailments;
- Review fumigation plan and programme.
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
- During August and September sea surface temperatures (SSTs) in waters surrounding Trinidad and Tobago mostly warmed, leading to positive anomalies and much warmer than average conditions overall. Warming is forecast to continue and is likely to maintain warmer than average SSTs. Warmer than average SSTs favour unsettled conditions and above normal rainfall totals for Trinidad and Tobago.
- Neutral El Niño–Southern Oscillation (ENSO) continued over the last 4 weeks but a transition from ENSO-neutral to La-Niña is favoured during the OND season. Recent cooling in the ENSO monitoring regions and model-outlooks strengthening the cooling over next three months, together have increased the chance of La Niña forming during OND. La Niña usually favours enhanced local rainfall for most of the latter half of the wet season, even though November tends to be drier than usual, when La Niña is present.
- Since August 01st, the North Atlantic Oscillation (NAO) fluctuated between its negative and positive phases but has return to its negative phase in the 3rd week of September. The NAO is forecast to remain in its negative-phase during most of October. This is likely to continue contributing to the warming of the SSTs in and around Trinidad and Tobago.
- The rainfall influencing phases of the Madden Julian Oscillation (MJO) linked to MJO RMM phase 8 through 2 are likely to favourably enhance rainfall totals over Trinidad and Tobago during the 2nd and 3rd weeks of October, if the current evolution of the MJO materializes.
The OND outlook is influenced by potential background or developing La Niña signals over the next eight weeks and above-normal sea surface temperature conditions in nearby and surrounding waters.
The October outlook is influenced by both the La Niña and warmer than usual SSTs signals, along with a wet regime associated with favourable Inter-Tropical Convergence Zone moisture flows, supported by possible MJO impacts.
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.