Dominica Weather

Seasonal Outlook: July – September 2017

Seasonal Outlook: July – September 2017

Looking back at the April – June 2017 Season

The season April – June (AMJ) is considered to be the transition period from the dry to the wet/ hurricane season. Above to normal rainfall total was accumulated for season. Day-time peak and average temperatures were above to normal, with normal minimum/ night-time temperatures.

Table 1: April – June (AMJ) 2017 Season
Normal (1982 – 2017)
  Canefield Airport Douglas-Charles Airport
Normal
234.0 to 387.5 mm
401.3 to 639.0 mm
AMJ 2017 Total
377.2 mm (normal)
817.5 mm (above normal)
Temperature
Average Maximum Normal
31.2oC to 31.8oC
29.7oC to 30.1oC
AMJ 2017 Average Maximum
32.1oC (above normal)
29.9oC (normal)
Average Mean Normal
27.5oC to 28.0oC
26.7oC to 27.1oC
AMJ 2017 Average Mean
28.6oC (above normal)
27.1oC (normal)
Average Minimum Normal
23.6oC to 23.9oC
23.7oC to 24.1oC
AMJ 2017 Average Minimum
23.8oC (normal)
24.1oC (normal)

El Nino Southern Oscillation (ENSO)

Recent Observations

In recent weeks, Sea Surface Temperatures (SSTs) in the equatorial eastern Pacific (NINO3.4) warmed to borderline El Niño conditions.

Model Forecast and Guidance

A majority of models suggest warm-neutral ENSO conditions during July – September (JAS) (60% confidence) and neutral or El Niño conditions by October – December (OND) 2017 (40-45% confidence).

Expected Impacts on Rainfall and Temperatures

The ongoing ENSO neutral state will have little effect on rainfall or temperatures. However, if El Niño manifests by OND 2017, odds are in favour of hotter conditions and less hurricane activity than usual in the latter part of the season, as well as drier weather with less extreme rainfall in the south and east of the region.

Mid-June 2017 Plume of Model ENSO Predictions Mid-June 2017 Plume of Model ENSO Predictions Mid-June IRI/CPC Model-Based Probabilistic ENSO Forecast Mid-June IRI/CPC Model-Based Probabilistic ENSO Forecast

Climate conditions in the Tropical North Atlantic and Caribbean

Recent observations: SSTs in the Tropical North Atlantic are above average (+0.5oC or more), especially near the West African coast. Trade winds have been slightly weaker than usual over the Tropical North Atlantic in May.

Expected Conditions: Current SST anomalies are expected to persist (or slightly weaken near Africa) throughout JAS and OND 2017.

Expected impacts: Positive SST anomalies tend to increase humidity and can therefore produce a probability shift towards above- to normal rainfall for JAS and OND, especially in northern portions of the region.

Seasonal Forecasts for July – September 2017

Rainfall Outlook

July - September and October - December 2017 Rainfall Outlook July – September and October – December 2017 Rainfall Outlook

Forecast: Drier than usual to usual conditions overall is forecast for the season July-August-September 2017. The forecast for the season October-November-December 2017, which is usually the wettest part of the year, is for wetter than usual to usual conditions overall. Chances of extremely dry or extremely wet conditions are quite low at this time (75% confidence).

Usually

July – September: normal accumulation range: Canefield Airport: 630.6mm to 847.6mm and Douglas-Charles Airport: 657.0 to 824.7mm.

October – December: normal accumulation range: Canefield Airport: 395.4 to 545.0mm and Douglas-Charles Airport: 733.0 to 950.7mm.

Probability for June – August 2017:

  • 25% chance of above normal
  • 35% chance normal
  • 40% chance of below normal

Probability for October – December 2017:

  • 40% chance of above normal
  • 35% chance normal
  • 25% chance of below normal

Wet Days and Wet Spells Outlook

Wet Days

July - September 2017 Wet Days Frequency Shift July – September 2017 Wet Days Frequency Shift

Table 2: July – September 2017 Wet Days(>1.0mm) Frequency Shift
Station Climatology (Wet days) Forecast (Wet days)
Canefield Airport 52 to 65 50 to 66
Douglas-Charles 56 to 69 57 to 74


Forecast
: An increase in the number of wet days (medium to high confidence) is expected.

Implication

  • Frequent rainfall disruptions of outdoor activities
  • Surface wetness makes environmental conditions more conducive to mosquito breeding and moisture related pests

7-Day Wet Spells

July - September 2017 7-day Wet Spells Frequency Shift July – September 2017 7-day Wet Spells Frequency Shift

Table 3: July – September 2017, 7 Day Wet Spells Frequency Shift
Station Climatology (7 day wet spell) Forecast (7 day wet spell)
Canefield Airport 3.7 to 7.4 3.8 to 8.1
Douglas-Charles 3 to 6.9 2.8 to 7.2


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

Implication: Recharge of large water reservoirs associated with wet season.

3-Day Wet Spells

Table 4: July – September 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 2.5 0 to 2.3
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 confidence).

Implication: There is potential for flash flooding.

Drought Outlook

Dought Outlook Dought Outlook

Forecast: There is no short term (April to September 2017) and long term (December 2016 to November 2017) drought concerns for Dominica at this time. Continue to monitor the situation in the coming months.

Temperature Outlook

Temperature Outlook Temperature Outlook

Forecast: Maximum (day-time) and minimum (night-time) temperatures averaged over the period July-August-September are forecast to be above to normal. Temperatures across the Caribbean are forecast to be uncomfortably hot for many, with high humidity and a high chance for heat waves until the end of October.

Usually: July – September: (Maximum temperature normal range: 31-32oC) (Mean temperature normal range: 27-28oC) (Minimum temperature normal range: 24-25oC).

Implications

  • Very likely increase in heat stress from heatwaves in human populations or livestock
  • More discomfort related to heat compared to recent months
  • Night-time heat more uncomfortable than in most other years
  • Warm conditions conducive for mosquito breeding and faster mosquito life cycles
  • Increased cooling needs

Probability

Maximum/day-time temperature Probability

  • 60% chance of above normal
  • 25% chance normal
  • 15% chance of below normal

Minimum/night-time temperature Probability

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

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Government of Dominica

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