TTMS: Dry Conditions Possible In Northwestern Trinidad Over Next 3 Months

The Trinidad and Tobago Meteorological Service (TTMS) is forecasting no concerns for impactful dry conditions over the next three months for most of both islands through June 2021, through the end of the 2021 Dry Season.

According to the TTMS, accumulated rainfall totals for the 3-months, January to March 2021 were much above the dryness indicator levels, as large amounts of rainfall in March literally washed away all indicators of borderline dry conditions, observed at the end of February, in Trinidad.

Notable, is the recovery of Tobago from worsening dry conditions at the end of February and in particular, recovery from a dry spell that was developing in the southwest of the island, at that time.

Observed dryness levels based on the rainfall differences from average, which have been standardized and expressed as the number of standard deviations less than average over January 2021 to March 2021 compared to the historical average for the same 3-month period. (TTMS)
Observed dryness levels based on the rainfall differences from average, which have been standardized and expressed as the number of standard deviations less than average over January 2021 to March 2021 compared to the historical average for the same 3-month period. (TTMS)

Predicted dryness levels for April to June 2021 based on the standardized rainfall difference between what is forecasted and the historical average rainfall, for the period of the forecast, while also considering actual observed rainfall for the last three months. (TTMS)
Predicted dryness levels for April to June 2021 based on the standardized rainfall difference between what is forecasted and the historical average rainfall, for the period of the forecast, while also considering actual observed rainfall for the last three months. (TTMS)

The Dryness Outlook for the 3-month period April to June 2021 indicates that there are no concerns for impactful dry conditions over the next three months for most of both islands. However, there is the possibility of borderline dry conditions developing in far northwest Trinidad, with dryness indicator values close to -0.5 on the Standardized Precipitation Index (SPI) scale, probable.

According to the TTMS, the outlook is based solely on rainfall and should be used only for guidance. In the TTMS’ Rainfall and Temperature Outlook issued in April 2021, the Office called for “April likely transitioning to drier than usual conditions across most areas. April to June (AMJ) 2021 is likely to be wetter than usual, with above-normal rainfall totals most likely,” for the second half of the 2021 Dry Season.

What is the Dryness Indicator?

The Dryness Indicator is a tool for keeping track of the level of dry conditions, rainfall deficit, and length of the dry period across Trinidad and Tobago. It is based on the TTMS’s Dry Spell and Meteorological Drought Policy which uses the Standardized Precipitation Index (SPI) to indicate dryness levels. The SPI is a simple measure of dryness based solely on the total rainfall for a given period, for example, over the last 60 days, compared with the long-term average rainfall for that period.

The colors on maps indicate observed levels of dryness based on the difference between observed and/or predicted rainfall and the average rainfall, which is then standardized and expressed as the number of standard deviations less than average. The colors moving from yellows to reds show increased levels of dryness. The grey areas indicate areas where the dryness is either very close to the average, average, or on the wet-side. In general, dryness concerns and negative impacts are expected when the dryness indicator’s value lies near -1.0. Concerns for dryness impacts increase as the size of the negative value increases.

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