El Nino Southern Oscillation (ENSO)

The strong 2015-16 El Nino has ended giving way to ENSO-Neutral conditions.

During mid-July 2016, the Tropical Pacific Sea Surface Temperature (SST) anomaly was slightly below zero indicating ENSO-neutral conditions. The key atmospheric variables also indicate neutral ENSO conditions. This includes near-average upper and lower level Tropical Pacific winds, as well as mainly near-normal cloudiness and rainfall patterns in the Central and Eastern Equatorial Pacific. Most ENSO prediction models indicate neutral ENSO conditions during July with likely development of La Nina during August or September with about 55-60% chance of La Nina conditions lasting towards the end of the 2016 Wet/Hurricane Season and into the 2017 Dry-Season. However the strength will most likely be weak.

Expected Impacts on Rainfall and Temperatures: A slight shift towards above- to normal rainfall is noted for much of the Caribbean due to slightly reduced winds in the upper atmosphere which allows for stronger, local showers to develop. A higher frequency of tropical storm likelihood during La Nina may also contribute to rainfall totals.

 

Climate conditions in the Tropical North Atlantic and Caribbean

Recent observations showed SSTs are 0.5 to 1^oC above-average within the Caribbean and higher just to the north. Positive SSTs anomalies are expected throughout the Tropical North Atlantic by August-September-October 2016. Trade wind strength is hardly predictable at seasonal time scales.

Expected impacts: Warm Atlantic Temperatures increases evaporation and local deep atmospheric convection, potentially increasing precipitation.

Note: Until around September, intrusion of dust and dry air associated with the Saharan Air Layer (SAL) and the trade winds may decrease rainfall chances. This is hardly predictable at seasonal time scales.

 

Regional Overview on Seasonal Forecasts for August to October 2016

Rainfall Outlook

There is low rainfall predictability for Dominica for the period August-September-October 2016.

Probability:

• 33% chance of above normal
• 33% chance normal
• 33% chance of below normal

 

Wet Days and Wet Spells Outlook

Wet Days

Table 1: August to October Wet Days(>1.0mm) Frequency Shift

Station	Climatology (Wet days)	Forecast (Wet days)
Canefield Airport	45 to 61	46 to 65
Douglas-Charles	57 to 70	59 to 79

Forecast: more wet days than normal (medium confidence).

Implication: Increasing surface wetness and disruptions of outdoor activities.

 

7-Day Wet Spells

Table 2: August - October 7 Day Wet Spells Frequency Shift

Station	Climatology (7 day wet spell)	Forecast (7 day wet spell)
Canefield Airport	3.5 to 6.4	2.8 to 6.8
Douglas-Charles	2.8 to 6.8	3.1 to 6.2

Forecast: There are no significant shifts in the number of 7-day wet spells and 7-day very wet spells (Low confidence).

 

3-Day Wet Spells

Table 3: August - October 3 Day Extreme Wet Spells Frequency Shift

Station	Climatology (3 day extreme wet spell)	Forecast (3 day extreme wet spell)
Canefield Airport	0 to 2.5	0 to 1.9
Douglas-Charles	0 to 1.1	0 to 1.4

Forecast: There are no significant shifts in the number of 3-day extreme wet spells (Medium confidence).

Implication: Flash flood potential developing.

 

Drought Outlook

Drought concerns at both the short term (May - October 2016) and long term (December 2015 – November 2016) have been alleviated. There are no drought concerns for Dominica.

 

Temperature Outlook

Air temperatures are expected to be above to normal. Night and day-time temperatures are expected to be warmer.