November 2021 – Tobago’s Driest On Record, Trinidad’s 2nd Driest

November is typically the second peak of the annual wet season in Trinidad and Tobago. November 2021, however, broke records for being quite the opposite. In Trinidad, November 2021 became the 2nd driest November on record, while it became the driest in Tobago. However, temperature-wise, it was near to below average across the country.

Tobago’s Driest November… Ever

The top three driest November’s in the 53-year history of records at Crown Point, Tobago. Data: Trinidad and Tobago Meteorological Service.

At Crown Point, Tobago, unprecedented dryness occurred in November 2021. For the 30 days of the month, only 36.0 millimeters of rainfall was measured. According to the Trinidad and Tobago Meteorological Service (TTMS), this registered as 85.5% less than the month’s average of 218.6 millimeters. It means that Crown Point had its lowest rainfall for November since records began in 1969. The Met Office has noted that typically, November is the wettest month in southwest Tobago.

The TTMS explained that the level of dryness witnessed during November 2021 at Crown Point has few precedents. None of the past Novembers at Crown Point had rainfall less than 50.0 millimeters, and only two had rainfall less than 100.0 millimeters. These were November 1995 and 1976 with 86.5 and 96.6 millimeters, respectively.

Fourteen of the last 22 Novembers had rainfall below the long-term average, with seven of these occurring in the previous ten years, while four of the last five years had Novembers with below-average rainfall totals.

The trend in Crown Point November Rainfall Performance shown as a percentage difference from the long-term average. (Trinidad and Tobago Meteorological Service)
The trend in Crown Point November Rainfall Performance shown as a percentage difference from the long-term average. (Trinidad and Tobago Meteorological Service)

Trinidad’s 2nd Driest November On Record

The top four driest November's in the 76-year history of records at Piarco, Trinidad. Data: Trinidad and Tobago Meteorological Service.
The top four driest November’s in the 76-year history of records at Piarco, Trinidad. Data: Trinidad and Tobago Meteorological Service.

Meanwhile, Trinidad recorded its second driest November on record at Piarco, with 81.4 millimeters of rainfall recorded over the 30-day-month. According to the TTMS, the average rainfall amount for November at Piarco is 221.9 mm (1991-2020 average). This places November 2021 rainfall total at 63.3% below the long-term average.

The Met Office has said, “This is not normal.” November 1952 with 70.2 millimeters remains the driest November on record. In the 76-year record since 1946, there were three previous Novembers when less than 100 millimeters of rain fell at Piarco. The last time this occurred was 41 years ago, in 1977, when 89.4 millimeters of rain fell during the month. Before this, apart from 1952, November 1950 produced 85.6 millimeters.

The trend in Piarco November Rainfall Performance shown as a percentage difference from the long-term average. (Trinidad and Tobago Meteorological Service)
The trend in Piarco November Rainfall Performance shown as a percentage difference from the long-term average. (Trinidad and Tobago Meteorological Service)

The TTMS also explained the abnormally low rainfall experienced during November 2021 at Piarco is a continuation of a drying trend observed in November rainfall over the last two decades. Fourteen of the last 22 Novembers (2000 to 2021) at Piarco had rainfall below the long-term average, and seven occurred in the last ten years. Notably, the last five Novembers each had rainfall below the long-term average.

However, the Met Office noted rainfall varied across the country. Still, the rainfall deficiencies and dryness observed in November affected the entire eastern half of Trinidad, extending into most areas of the western half of Trinidad and all of Tobago. The exception was northwest Trinidad in the Diego Martin area. The area received heavy bursts of rainfall during the second week of November that produced just about 174 millimeters over 24 hours from 8:00 AM on the 11th to 8:00 AM on the 12th. This episode of torrential rainfall mostly accounted for the area receiving 51% more rainfall than the month’s long-term average for the area.

Why was it so dry? Climate change.

The TTMS said the significantly below average rain that fell in November followed eight extremely wet months, out of the nine months from February to October, that produced above-average rainfall, which was only broken by June with near-average conditions.

This observed recent drying trend across Trinidad and Tobago during November is consistent with expected climate change impacts that are anticipated to influence a greater frequency of drier than usual wet season months in Trinidad and Tobago.

The Trinidad and Tobago Meteorological Service is associating November’s dryness with a strong and persistent pattern of upper-level subsidence or sinking air (associated with positive velocity potentials), which acted as a cap to cloud development.

Temperatures

Meanwhile, temperatures in November were relatively low compared to the historical record on average. The mean monthly temperature was 0.3°C cooler than the average (27.7°C). Similarly, the mean night minimum temperature was 0.6°C cooler than the average of 23.6°C, while the mean maximum daytime temperature matched the long-term average of 31.8°C. The hottest temperature of the month at Piarco was 33.0°C on the 24th, while it reached 32.9°C on the 22nd in Tobago. The coolest night in Trinidad was the 17th, with a minimum temperature of 22.1°C, while it was 23.7°C on the 10th in Tobago.

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