Seasonal Outlook May - June - July 2017

Looking back at the February-March-April 2017 Season

The dry season runs from December to May when the seas are relatively cooler and thunderstorms and rainfall activities are relatively low. Rainfall accumulated at both the Canefield and Douglas-Charles Airports for the season February-March-April 2017 was above normal. Above to normal maximum temperatures (day-time temperatures), above normal mean temperatures and normal to below normal minimum temperatures (night-time temperatures) were recorded.

Seasonal Outlook (May-June-July (MJJ) 2017)

El Nino Southern Oscillation (ENSO)

Recent Observations:

In recent months, sea-surface temperatures (SSTs) in the Eastern Equatorial Pacific (NINO3.4) warmed to slightly above average.

Model forecast and guidance:

Majority of models suggest warm-neutral ENSO conditions during MJJ (55% confidence) and possibly El Niño conditions by August-September-October (ASO) 2017 (70% confidence).

Note: ENSO models have a notoriously hard time predicting ENSO at this time (i.e. the ‘spring predictability barrier’).

Expected impacts on rainfall and temperatures:

With current neutral ENSO conditions, little effect on rainfall or temperatures is expected. However, if El Niño manifests by August-September-October 2017, odds are in favour of hotter conditions and less hurricane activity than usual, as well as drier weather with less extreme rainfall (except in the northern-most parts of the region).

Climate conditions in the Tropical North Atlantic and Caribbean

Recent Observations:

The Tropical North Atlantic SSTs are now near to slightly above average (0-0.5°C) in most places, but remained above average north of the islands. Slight anomalous warming is expected to persist throughout MJJ and ASO 2017. Trade winds have been slightly stronger than usual over the Tropical North Atlantic.

Expected Conditions: SSTs are expected to warm until September, but the warm anomalies are forecast to be less extreme than in previous years. Note also that episodes of Saharan dust blowing into the region are likely until September, but they are hardly predictable at this time.

Expected impacts: Positive SST anomalies tend to increase humidity and can therefore produce a probability shift towards above- to normal rainfall for MJJ and ASO 2017 across the northern portions of the region.

Regional Overview on Seasonal Forecasts for May - June - July 2017

Rainfall Outlook

Forecast:

Uncertainties continues for the next season’s rainfall expectation, however, below to normal rainfall total is expected for the second half of the wet season (Normal range for May to June- approximately 400 to 600mm) (Normal range for August to October- approximately 600 to 900mm)

Probability for May - June - July 2017

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

Probability for August - September - October 2017

  • 20% chance of above normal
  • 35% chance normal
  • 45% chance of below normal

Wet Days and Wet Spells Outlook

Wet Days

AMJ 2017 Wet Days Frequency Shift

Table 1: May - June - July 2017 Wet Days(>1.0mm) Frequency Shift
Station Climatology (Wet days) Forecast (Wet days)
Canefield Airport 35 to 60 36 to 59
Douglas-Charles 46 to 66 44 to 67

Forecast: No significant change from the usual (low to medium confidence) is expected.

Implication: Increasing surface wetness improves environmental conditions for mosquitoes and moisture related pests.

7-Day Wet Spells

MJJ 2017 7-day Wet Spells Frequency Shift

Table 2: May - June - July 2017 - 7 Day Wet Spells Frequency Shift
Station Climatology (7 day wet spell) Forecast (7 day wet spell)
Canefield Airport 2.1 to 5.2 2.7 to 7.2
Douglas-Charles 1.7 to 4.7 2.1 to 6.0

Forecast: An increase in 7-day wet and very wet spells frequency (low to medium confidence).

IMPLICATION: The recharge of large water reservoirs related to the onset of the wet season.

3-Day Wet Spells

MJJ 2017 frequency of extreme (1%) 3-day Wet Spells

Table 3: May - June - July - 3 Day Extreme Wet Spells Frequency Shift
Station Climatology (3 day extreme wet spell) Forecast (3 day extreme wet spell)
Canefield Airport 0 to 1.1 0 to 0.9
Douglas-Charles 0 to 1 0 to 1.1

FORECAST: There is little indication of change in frequency for 3-day extreme wet spells (low to medium confidence).

IMPLICATION: Flash flood potential is becoming a concern.

Drought Outlook

FORECAST: The drought watch alert issued for Dominica late March was discontinued. A drought watch alert remained for the rest of the Lesser Antilles. Currently there are no short term (February to July 2017) and hydrological (June 2016 to May 2017) drought concerns for Dominica. Continue to monitor the situation in the coming months.

Temperature Outlook

FORECAST: Night and day-time temperatures are forecast to be uncomfortably hot for many islands, with high humidity and a high chance for heat waves.

NOTE: This scenario becomes more likely and heat more severe if a moderate or strong El Niño manifests by August.

(Maximum temperature normal range: 30-32°C) (Mean temperature normal range: 27-29°C)  (Minimum temperature normal range: 24-25°C)

Maximum/day-time temperature Probability

  • 45% chance of above normal
  • 35% chance normal
  • 20% chance of below normal

Minimum/night-time temperature Probability

  • 50% chance of above normal
  • 30% chance normal
  • 20% chance of below normal