Seasonal Forecast: August to October 2021

Seasonal Forecast: August to October 2021

Date of Issue: August 6th, 2021


Ø Seasonal Forecast: August-September-October (ASO)



As the wet season/ tropical cyclone season comes to its peak, rainfall is likely to be as high as usual. Therefore, the usual increase in wet days (wet day: greater than or equal to 1.0mm of rainfall) and frequency of wet spells is anticipated.

This may result in an increase in disruption of outdoor activities and in the incidence of moisture-related pests and diseases. The potential for flash floods and associated hazards is expected to be high or even extremely high. The probability of a 7-day dry spell is very low to negligible.



 The Caribbean Heat Season peaks during ASO and both night-time minimum and daytime maximum temperatures are likely to be the usual or higher. At least 6 heatwaves days are possible on the island during August. There is a 50-80% chance of at least 15 heatwave days during the period, ASO, which is usual.  A heatwave day is registered when the daily high is equal to or exceeds 32.9°C at Canefield and 31.5°C at Douglas-Charles.

Heat stress in the population and in livestock is expected to peak during heatwaves. However, this is expected to be less severe than that which occurred during 2020. Temperatures should quickly cool to become seasonably comfortable in November.


Ø Influencing Factors

1.      El Niño Southern Oscillation (ENSO)


Recent observations: Neutral ENSO conditions are in place, with near average Sea Surface Temperatures (SSTs) in the eastern Pacific.


Model forecast and guidance: Models favor ENSO neutral conditions through ASO (50-60% confidence). However, large uncertainties exist as to whether this will persist through Nov-Dec-Jan or whether La Niña conditions will return.


Expected impacts on rainfall and temperatures: ENSO neutral offers little predictability and reduces the confidence of the forecasts at this time. If La Niña re-emerges, the chance for more rainfall and increased tropical cyclone activity increases.


 2.  Climate conditions in the Tropical North Atlantic (TNA) and Caribbean Sea


Recent observations: SSTs are near average in the Caribbean Sea and the Tropical North Atlantic (TNA) and remains about 0.5°C above average in the sub-tropical North Atlantic.

Expected conditions: SSTs to increase to about 0.5°C above average throughout the season and into January 2022.

Expected impacts: Warm SSTs in and around the Caribbean tend to contribute to higher air temperatures, above-average humidity, higher tropical cyclone activity and seasonal rainfall totals with increased frequency of extreme rainfall.



See table below with Climatological Normal/ Averages



Accumulated Rainfall (30 years)


Canefield Airport

Douglas-Charles Airport


507.1 to 733.5mm

708.6 to 964.8mm

Wet days Normal

45 to 61

57 to 71

Forecast (ASO 2021)

44 to 60

55 to 71

7- Day Wet Spell Normal

4 to 6

4 to 7

Forecast (ASO 2021)

3 to 9

4 to 7

7 day dry spell


0 to 1

Temperature (15 years)

Average Maximum

32.0 to 32.5°C

30.7 to 31.2°C


27.9 to 28.2 °C

27.5 to 27.8°C

Average Minimum

23.8 to 24.1°C

24.1 to 24.3°C