Seasonal Outlook - March - May 2017

 

Looking back at the December 2016 -January-February 2017 Season

The dry season runs from December to May when the seas are cooler and thunderstorms and rainfall activities are relatively low. Rainfall accumulated at the Canefield Airport for the season December 2016-January-February 2017 was above its 30yr normal while the Douglas-Charles Airport accumulated total was below its 30yr normal. Both stations recorded above to normal air temperatures for the season.

Seasonal Outlook (March-April-May 2017)

Influencing Factor

El Nino Southern Oscillation (ENSO)

Recent Observations:

ENSO-neutral conditions have returned, with slightly below-average sea surface temperatures (SSTs) observed across the Central Equatorial Pacific and above-average SSTs increasing in the Eastern Pacific.

Model Forecast and Guidance:

Most models predict the continuation of ENSO-neutral (3-month average Niño-3.4 index between -0.5°C and 0.5°C) through the Northern Hemisphere summer. However, a few dynamical models anticipate an onset of El Niño towards the end of the dry season into the wet season (dry season-December to May, wet season-June to November).

Expected Impacts on Rainfall and Temperatures:

ENSO neutral conditions have little effect on rainfall or temperatures. However, if El Niño manifests by June-July-August, odds are in favour of drier weather with less extreme rainfall than usual for the first half of the wet season.

Climate conditions in the Tropical North Atlantic and Caribbean

Recent Observations: Recent observations showed SSTs up to 0.5°C above-average within the Caribbean and the Tropical North Atlantic east of the islands. SSTs in the far northwest of the region are far above average. Trade winds have been slightly stronger than usual over the Tropical North Atlantic.

Expected Conditions: SSTs are expected to return to values closer to average in the Caribbean Sea and further east by June-July-August. Strength of trade winds is hardly predictable at seasonal time scales.

Expected impacts: A slight probability shift towards above to normal rainfall is expected for March-April-May 2017 as positive SST anomalies in the Caribbean Sea and Tropical North Atlantic tends to increase humidity over the region which in turn can lead to increased rainfall. This influence may subside by June-July-August.

Regional Overview on Seasonal Forecasts for October to December 2016

Rainfall Outlook

Forecast: Slightly above to normal rainfall totals can be expected at least up to April 2017. However, there are uncertainties beyond that. (Normal range for March to May- approximately 250 - 400mm)

Probability:

  • 35% chance of above normal
  • 35% chance normal
  • 30% chance of below normal

Wet Days and Wet Spells Outlook

Wet Days

Table 1: March-April-May 2017 - Wet Days(>1.0mm) Frequency Shift
Station Climatology (Wet days) Forecast (Wet days)
Canefield Airport 21 to 35 21 to 37
Douglas-Charles 36 to 60 35 to 59

Forecast: No significant change in the usual amount of wet days (low confidence) is expected.

7-Day Wet Spells

Table 2: March-April-May 2017 - 7 Day Wet Spells Frequency Shift
Station Climatology (7 day wet spell) Forecast (7 day wet spell)
Canefield Airport 0 to 2 0 to 2.5
Douglas-Charles 1.3 to 3.4 1.1 to 4

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

Implication: The build-up of usual dry season impacts on water availability should be slower than usual.

3-Day Wet Spells

Table 3: March-April-May 2017 - 3 Day Extreme Wet Spells Frequency Shift
Station Climatology (3 day extreme wet spell) Forecast (3 day extreme wet spell)
Canefield Airport 0 to 0 0 to 0
Douglas-Charles 0 to 1.6 0 to 1.6

Forecast: No change in frequency for 3-day extreme wet spells (low confidence).

Implication: Flash flood potential is not a major concern until the end of April

Drought Outlook

There are no drought concerns for Dominica both at the short term (December 2016- May 2017) and long term (June 2016 –May 2017).

Temperature Outlook

Forecast: Temperatures across the Caribbean are forecast to gradually rise and become more uncomfortable throughout the period. Heat discomfort will probably grow more slowly in the Windward than at this time in the past couple of years. The chances of heat waves are appearing in May and June for many islands. (Maximum temperature normal range: 29-31°C) (Mean temperature normal range: 26-28°C) (Minimum temperature normal range: 22-23°C)

Probaility:

Maximum/day-time temperature Probability

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

Minimum/night-time temperature Probability

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