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



ISSUED AT: 02:47 PM

Date: Monday 4th of February 2019

Key Messages

  • Rainfall shortages were observed at all, except one of seven selected stations during November 2018 and at all of the selected stations during December 2018. At Piarco, 47.9 mm or 68.3% less than the monthly average rainfall (151.6mm) was recorded for December, which placed December 2018 as the 2nd driest December at Piarco since 1946 (73 years). At Crown Point,  55.8 mm of rainfall or 44.9% of the monthly average (124.3mm) was observed, which placed Decmber 2018 as the 6th driest December on record since 1969 (50 years).
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Trinidad and Tobago Dry/Wet Spell Monitor and Outlook by End of March 2019



ISSUED AT: 02:47 PM

Date: Monday 4th of February 2019

Key Messages

  • Rainfall shortages were observed at all, except one of seven selected stations during November 2018 and at all of the selected stations during December 2018. At Piarco, 47.9 mm or 68.3% less than the monthly average rainfall (151.6mm) was recorded for December, which placed December 2018 as the 2nd driest December at Piarco since 1946 (73 years). At Crown Point,  55.8 mm of rainfall or 44.9% of the monthly average (124.3mm) was observed, which placed Decmber 2018 as the 6th driest December on record since 1969 (50 years).
  • Rainfall deficiencies continued to affect the islands during January 2019. At Piarco 18.4 mm or 76.2% less than the monthly average rainfall was recorded for January, placing January 2019 as the  5th driest January in 73 years. At Crown Point, a new record was set for January with 3.0 mm of rainfall recorded which was  95.7% less than average. This placed January 2019 as the driest January in 50 years at Crown Point.
  • The dry spell/drought monitor shows the 2-month Standardized Precipitation Index (SPI) at the selected stations over the months of November to December 2018 were negative and ranged from -0.91 to -2.0.
  • Negative SPI's continued over the  2-month period December 2018  to January 2019 and ranged from -1.6 to 2.0 at the selected stations. As a result, the early warning dry spell/drought monitor is now at meteorological drought warning.
  • The 3-month Dry Spell/Drought Outlook for the period ending March 2019 shows SPIs ranging between -1.2 to -2.0, which suggest the current dry spell is likely to continue.

Drought/Dry-Spell Monitor

The Standardized Precipitation Index for the 12 months ending December 2018 shows rainfall totals were in the wet categories at two of the selected stations in Trinidad while it was in the dry categories at the remaining five selected stations across the country (see Figure 1).

Figure 1. Shows 12-month Standardized Precipitation Index (SPI) at selected stations. Downward pointing arrows represent negative SPIs and the level of  of dryness observed. Upward pointing arrows represent positive SPIs and the degree of level of wetness observed.

 

Over the 2-month period, November to December 2018, Trinidad and Tobago observed significant rainfall deficits indicated by moderately dry  to exceptionally dry conditions on the 2-month SPI monitor (see Figure 2). Negative SPIs over the two months  ranged from -0.91 to -2.0, placing Trinidad and Tobago in a dry spell/drought watch on the dry spell/drought early warning system by the end of December. 

Figure 2. Shows 2-month Standardized Precipitation Index (SPI) at selected stations for November to December 2018. Downward pointing arrows represent negative SPIs and the level of dryness observed.

Drying continued over the 2-month period December 2018 to January 2019.  During this period Trinidad and Tobago observed significant rainfall deficits as indicated by extreme to exceptional dry conditions on the 2-month SPI monitor (see Figure 3), placing the country in a meteorological drought. 

Figure 3. Shows 2-month Standardized Precipitation Index (SPI) at selected stations for December 2018 to January 2019. Downward pointing arrows represent negative SPIs  and  the level of dryness observed.

Drought Indicator Outlook:

  • The 3-month Standardized Precipitation Index (SPIs) dry spell/drought outlook indicator for the period ending March 2019 shows impactful drying is likely to persist up to March month end (see Figure 4).
  • 3-month SPIs by the end of March are expected to persist as negative and range between -1.50 and - 2.1.
  • In general, impacts from the dryness are expected if SPIs during the dry season are lower than -1.0 (dry spell or worse).

Figure 4. Shows 3-month Standardized Precipitation Index (SPI) outlook  for the 3-month period ending March 2019. Brown colours represent the level of dryness expected.

Guide

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 predefined timescales, such as 2-months, 3-months, 6-months, 12-months. Negative SPI values 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.

Meaning of  meteorological drought

A meteorological drought means that a place receives much less rainfall than normal over a few months or even longer. 

A meteorological drought event in Trinidad and Tobago starts when the 2-month SPI value reaches -1.5 and continues over  two overlapping 2-month periods. The drought ends when the SPI becomes positive again.