Rainfall and Temperature Outlook for Trinidad and Tobago, July to September 2020



ISSUED AT: 11:01 AM

Date: Monday 29th of June 2020

Key Messages
  • The wet and hurricane seasons are only one month old and already the country has been affected by adverse weather events, which have caused damages;
  • July to September rainfall outlook indicates the  month of July is likely to be wetter than average;
  • The 3-month period, July to September is likely to bring near-normal rainfall conditions in northeast and southeast Trinidad, and above normal conditions in southwest Trinidad, parts of the northwest Trinidad and all of Tobago;
  •  July to September is likely to get a slight increase in the frequency of wet days, 7-day wet spells and moderate and heavy rainfall days;
  •  This means there will likely be an increased number of adverse-weather events to contend with, as the period is likely to bring increased unsettled conditions;
  • The second three (3) months (October  to December) is favoured to be wetter than usual with above-normal rainfall totals likely;
  •  The temperature outlook for the wet season strongly indicates above-normal temperatures are likely with warmer than average maximum day and minimum night temperatures expected. The risk for hot days and short-duration hot spells remain elevated for the August to October period.

Likely Impacts

  • Elevated flooding risks continue but especially for flood-prone areas; as localized heavy  rainfall and prolonged wet spells will increase flash-flooding potential  in high-risk/flood-prone areas and within watersheds with narrow valleys and steep hill-sides;
  • The country is likely to receive very high rainfall totals, since July and August are two of the wettest months of the wet season. High wind events during adverse weather events are likely;
  • Increased rainfall tend to aid mosquitoes breeding and spikes in vector borne diseases;
  • Higher than usual temperatures during the peak of the heat-season can lead to excessive heat which can amplify existing health conditions in vulnerable persons.

 


Rainfall and Temperature Outlook for Trinidad and Tobago, July to September 2020



ISSUED AT: 11:01 AM

Date: Monday 29th of June 2020

Near-  to  Above-Normal Rainfall Likely During July to September 2020

 
Key Messages
  • The wet and hurricane seasons are only one month old and already the country has been affected by adverse weather events, which have caused damages;
  • July to September rainfall outlook indicates the  month of July is likely to be wetter than average;
  • The 3-month period, July to September is likely to bring near-normal rainfall conditions in northeast and southeast Trinidad, and above normal conditions in southwest Trinidad, parts of the northwest Trinidad and all of Tobago;
  •  July to September is likely to get a slight increase in the frequency of wet days, 7-day wet spells and moderate and heavy rainfall days;
  •  This means there will likely be an increased number of adverse-weather events to contend with, as the period is likely to bring increased unsettled conditions;
  • The second three (3) months (October  to December) is favoured to be wetter than usual with above-normal rainfall totals likely;
  •  The temperature outlook for the wet season strongly indicates above-normal temperatures are likely with warmer than average maximum day and minimum night temperatures expected. The risk for hot days and short-duration hot spells remain elevated for the August to October period.
 

 Likely Impacts

  • Elevated flooding risks continue but especially for flood-prone areas; as localized heavy  rainfall and prolonged wet spells will increase flash-flooding potential  in high-risk/flood-prone areas and within watersheds with narrow valleys and steep hill-sides;
  • The country is likely to receive very high rainfall totals, since July and August are two of the wettest months of the wet season. High wind events during adverse weather events are likely;
  • Increased rainfall tend to aid mosquitoes breeding and spikes in vector borne diseases;
  • Higher than usual temperatures during the peak of the heat-season can lead to excessive heat which can amplify existing health conditions in vulnerable persons.

 

 

 

Early  Actions & Preparedness

  • Closely monitor the  Trinidad and Tobago Meteorological Service weather forecasts;
  • Strengthen community coordination with disaster management personnel;
  • Prepare contingency plans for adverse weather events, including high wind events;
  • Persons living in flood risk areas should continue their flood planning and  preparedness efforts;
  • 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 be 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 July to September 2020 (JAS) 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 JAS period rainfall totals during the historical period used to produce the outlook.

  • In the short term, the month of July is likely to be wetter than average for all of Trinidad and Tobago;
  • Near to above normal conditions are likely for Trinidad and Tobago over the three months July to September;
  • Wetter than average conditions are likely for southwest Trinidad, parts of northwest Trinidad and all of Tobago; while near average conditions are expected for most of southeast and northeast Trinidad;
  • This means the country is likely to receive 3-month rainfall totals that are between 75% and 125% of the long term averages in areas where near-normal rainfall is expected and greater than 125% where above normal is expected. For instance, at Piarco, this means accumulated JAS rainfall totals greater than 705.0 mm and at Crown Point totals greater 633.0mm.

Figure 2: The map shows the chances for extremely dry conditions over the next three months, July to September 2020. Extremely dry conditions refer to the lowest 10% of July to September seasonal total rainfall amounts in the historical record.

  • The likelihood of drier than usual conditions is low;
  • The chance for July to September 2020 to be extremely dry is very low, less than 10% chance.
 

Figure 3: Possible accumulated rainfall totals with the highest chance of occurring during July to Sepetmber 2020.

  • Most of Trinidad and Tobago is likely to receive rainfall in excess of 500.0 mm over the three months July to  September 2020;
  • Areas in northeast Trinidad are likely to receive the highest rainfall totals (near 1000.0 mm), while  a few areas on the west coast of Trinidad, as well as, in southwest Tobago are likely to receive the lowest accumulated rainfall totals (near 500.0 mm);
  • There is a 55% chance for 6-8 days with rainfall totals greater than or equal to 25 mm and a 45% chance for up to 2 days with rainfall greater than or equal to 50 mm during JAS 2020;
  • Both islands are likely to receive 45-55 wet days during JAS (usually out of 92 days in JAS the average is 47-59 wet days for Trinidad and 36-51 for Tobago);

  • The risk of flooding remains elevated for the period July to September.

 

Figure 4: Possible rainfall totals with the highest chance of occurring during July 2020.

 

  • July 2020 rainfall totals are likely to range from as low as 161.0 mm in a few areas in southwest and northwest Trinidad to near 330.0 mm in a few areas in the northeast;
  • In Tobago, areas in the southwest and northeast are likely to receive rainfall totals between 161 and 228 mm.

 

Figure 5:  Category of rainfall most likely for October to December (OND) 2020 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.

  • The preliminary outlook indicates that October to December 2020 (OND) is strongly expected to be wetter than usual with above-normal rainfall totals as the most likely category;
  • The chances for above-normal rainfall are greater than 51% for most areas of the country;

  • Above-normal rainfall for this time of the year is a substantial amount of rainfall;

  • The risk of flooding during OND is further elevated.

 

The Temperature Outlook

  • The temperature outlook for the 2020 wet-season tilts quite strongly towards above-normal temperatures;
  • Daytime temperatures, including maximum temperatures during July to September are likely to be warmer than average (greater than 65% chance);

  • Similarly, night-time temperatures, including minimum temperatures are likely to be warmer than average (greater than 65%);

  • Chances are elevated for an increase in the frequency of hot-days and short-duration hot spells during August and September, with the risk being highest in September. A hot-day is a day when the maximum temperature equals or exceeds 34oC in Trinidad and 32oC in Tobago. A short-duration hot spell is 3 or more consecutive hot days.

  • Usually, the peak of the local heat-season and the riskiest period for hot days and hot spells is during August to October.

Figure 6: 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 July to September 2020.  The colour-coded bar-graph with the numbers to the right gives the likelihood for each forecast category to occur.

Likely Implications

  • An enhanced likelihood for near- to above-normal rainfall during JAS suggests  increased chances for flooding and increased flood-risks in flood-prone areas;
  • Localized moderate to heavy  rainfall days and prolonged wet spells during JAS could trigger flash-flooding in high-risk/flood-prone areas and within watersheds with narrow valleys and steep hill-sides;

  • Expect a continuation of increased recharge rates, surface water flows and river levels;

  • Possible increased turbidity and degraded water quality on heavy rainfall days;

  • More reliable rains for agriculture but the excess rainfall can lead to waterlogging of agricultural fields;

  • Increased rainfall, mixed with warm and humid conditions tend to 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;

  • An increase in surface water ponding can promote mosquito breeding, which can lead to higher risks for spikes in vector borne diseases;

  • Increased adverse weather events is likely to also produce an increase in high wind events;

  • Higher than usual and extreme temperatures can lead to relatively excessive heat for Trinidad and Tobago during the peak of the local heat season, which can amplify existing health conditions in vulnerable persons and worsen chronic health conditions in others;

  • Should JAS get above-normal rainfall, soils are likely to become highly saturated, river levels are also likely to become high; and hence, the enhanced likelihood for above-normal rainfall during October to December will further elevate the risks for flash and riverine floods.

 

Early Actions & Preparedness

General Public

  • Closely monitor the  Trinidad and Tobago Meteorological Service weather forecasts;
  • Strengthen community coordination with disaster management personnel;
  • Prepare contingency plans for events, including high wind events;
  • 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;
  • 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.

Drainage

  • Ramp-up de-silting and cleaning of drainage systems, water channels, outlets and river mouths. Pay attention to areas of rock fall which may be indicative of potential landslides.

Disaster Risk Management Sector

  • Put  in place the necessary measures to ensure communities are sensitized;
  • Continue preparedness for the increase in rainfall and the associated negative impacts;
  • Continue to review contingency plans and early warning information dissemination channels;
  • Engage vulnerable communities in disaster plans and strategies;
  • Continue to engage the media for delivery of suitable messaging and advice on the outlook.

Water and Energy sector

  • Update flood action plans and continue water conservation awareness messaging;
  • Revisit contingency plans and ramp-up de-silting of major rivers and reservoirs;
  • Remove dry branches, rotting trees and tree-overhang near electrical power wires.

Health Sector

  • Revisit contingency plans to manage possible spikes in vector-borne diseases;
  • Improve the usage of early excessive heat climate outlook information in plan of action.

Agriculture & Food Security Sector

  • Raise awareness on agriculture pest and disease control measures;
  • Escalate flood mitigation action plans and removal of rotten trees.

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.

 

Climatic Influencers and Context of the Outlook

  • ENSO-neutral-cool conditions currently exist across the equatorial Pacific Ocean. During the last 4 weeks the Niño3.4 Index anomaly (in the central tropical Pacific) was -0.4˚C (neutral-cool), a relatively sizable decrease from the previous month;
  • Most of the key models and the consensus outlook favour ENSO-neutral during July with equal chances for ENSO-neutral to persist or La Niña conditions to develop during August to October, but this is not guaranteed;
  • La Niña or ENSO-neutral-cold conditions during the local wet season tend to tilt the odds in favour of enhanced rainfall occurrence  in Trinidad and Tobago;
  • Sea surface temperatures (SST) in waters in relatively close proximity to Trinidad and Tobago are warmer than average for this time of the year. Warmer than average SSTs in waters to the east of Trinidad and Tobago tend to have a positive influence on local rainfall;
  • For most of June, the North Atlantic Oscillation (NAO) was in its negative phase and this is likely to continue in the short-term. A negative NAO tends to aid warmer than usual  SSTs in the waters, in and around Trinidad and Tobago;
  • The Madden Julian Oscillation (MJO), is one of the key climate influencers for suppression or enhancement of rainfall at the sub-monthly scale, but is not expected to play an active role in influencing localized high-impact rainfall events during the first three weeks of July.

The outlook is based on seasonal climate models output and known seasonal climate influencers. The outlook is in reasonable agreement with several of the global climate models; and reflects the influence of warmer than average SSTs in waters around T&T and ENSO-neutral cool conditions with potential to transition to La Nina.