Trinidad and Tobago Dry/Wet Spell Monitor and Outlook By End of September 2019



ISSUED AT: 03:58 AM

Date: Saturday 20th of July 2019

Key Messagess:

  • The 3-month Dry/Wet Spell Outlook for the July to September 2019 shows Standardized Precipitation Indices are likely to range between 0.1 and -0.5 across Trinidad and Tobago. As such, the early warning short-term dry-spell outlook places Trinidad and Tobago at the little to no concern categories.
  • During June 2019, rain...


Trinidad and Tobago Dry/Wet Spell Monitor and Outlook by End of September 2019



ISSUED AT: 03:58 AM

Date: Saturday 20th of July 2019

Key Messagess:

  • The 3-month Dry/Wet Spell Outlook for the July to September 2019 shows Standardized Precipitation Indices are likely to range between 0.1 and -0.5 across Trinidad and Tobago. As such, the early warning short-term dry-spell outlook places Trinidad and Tobago at the little to no concern categories.
  • During June 2019, rainfall shortages were observed at all of the seven selected rainfall stations within the catchment areas of the country. 
  • 12-month (July 2018-June 2019) rainfall totals percentage difference from average ranged from negative 3% to negative 46%, with Tobago receiving the largest deficits.
  • The dry spell/drought monitor shows the 3-month Standardized Precipitation Index (SPI) at selected stations over the months, April to June 2019 ranges from -0.13 to – 0. 89 which represents rainfall totals that are less than the average.

Dry/Wet Spell 3-Month Outlook:

  • Figure 1 shows the 3-month dry-spell/wet-spell for July to September 2019 indicates little to no concern for short-term dryness or dry spell conditions across Trinidad and Tobago, based on Standardized Precipitation Index forecast.
  • 3-month SPIs by the end of September are expected to be slightly negative and range between - 0.1 to - 0.4.
  • In general, impacts from the dryness are expected if SPIs during the wet season are lower than -1.5 (dry spell or worse).

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1.  Shows the dry/wet spell outlook for the three months July to September 2019 

 

Drought / Dry-Spell Monitor

Figure 2 shows the SPI-based dry spell monitor over the 12 months July 2018 to June 2019 indicating rainfall totals were on the deficit side of the monitoring scale. At selected stations within Trinidad and Tobago catchment areas, negative Standardized Precipitation Index (SPI) were observed.

   

Figure 2.  Shows rainfall deficiencies (dry) or surpluses (wet) for the 12 months July 01, 2018 to June 30, 2019

 

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Figure 3.  Shows rainfall totals percentage of average for the 12 months July 01, 2018 to June 30, 2019.

Figure 3. shows that at selected rainfall stations across Trinidad and Tobago catchment areas, the percent of average rainfall totals for the 12 months July 01, 2018 to June 30, 2019 were below average when compared with the 1981-2010 average. Percent of average differences ranged from ranged from negative 3% to negative 46%, with Tobago receiving the largest deficits.

 

Figure 4. shows that over the 3-month period April 2019 to June 2019 selected stations within Trinidad and Tobago catchment areas observed rainfall total deficits, indicated by dry to moderately dry conditions on the 3-month SPI monitor scale.

Figure 4.  Shows rainfall deficiencies or surpluses for the 3 months April 01, 2019 to June 30, 2019

Guide For  Interpreting This Product

Meaning of drought

A drought means that a place receives much less rainfall than normal over a few months or even longer and the 3-month SPI is -1.5 or less.

Standardized Precipitation Index   

The Standardized Precipitation Index (SPI) is an index showing the severity and rarity of dryness or wetness of an area and is used to monitor and estimate dryness and wetness on different timescales. Negative values of SPI indicate less than median rainfall and drier conditions; positive values indicate greater than median rainfall and wetter conditions. The SPI values can be interpreted as the number of standard deviations by which the observed rainfall deviates from the long-term average. In general, dryness impacts are expected when the value of the 3-month SPI lies near -1.0. As the SPI value becomes less than -1.0, the severity of impacts increases. For Trinidad and Tobago, extreme dryness is considered to occur when negative SPIs are lower than -1.25 in the dry season and near -1.5 or lower in the wet season.