The weather of the southeastern Caribbean is governed by a small number of large-scale systems. Understanding the mechanisms explains the seasons, the rainfall distribution and the storm risk more usefully than a table of monthly averages.
| Dominant flow | the northeast trade winds |
|---|---|
| Seasonal driver | migration of the tropical rain belt |
| Rainfall pattern | strongly shaped by topography |
| Position | southern end of the hurricane belt |
The trade winds
Persistent easterly flow driven by the pressure gradient between the subtropical high and the equatorial trough.
Effects on the island:
- A consistent easterly wind for most of the year
- The windward and leeward distinction that shapes coastal conditions
- Moderated temperatures, since the air arrives over open ocean
- Sea state differences between the two coasts
The consistency is the point. Unlike mid-latitude weather, which arrives from varying directions, the dominant flow here is reliably easterly, which is why the same coast is sheltered day after day.
The seasons
Not defined by temperature, which varies little through the year, but by rainfall.
- A drier season when the subtropical high is stronger and the rain belt sits further south
- A wetter season when the tropical rain belt migrates north over the region
- Transitional periods at either end
- Diurnal patterns — convective showers building through the day
The mechanism to understand is the seasonal migration of the tropical rain belt. It follows the sun's movement with a lag, and its position over or away from the island determines the season — which is why the seasons here are wet and dry rather than warm and cold.
Topographic rainfall
The most consequential local effect and the reason rainfall varies dramatically across a small area.
- Moist air is forced upward over the mountainous interior
- It cools, condenses and rains on the windward slopes and highlands
- The leeward side receives less, in the rain shadow
- Total rainfall varies several-fold between coast and interior
The practical consequences reach into everything else in this reference. Water supply catchments are in the wet interior; the driest areas are coastal and often the most settled; and agricultural suitability follows the rainfall gradient rather than the map distance.
It also explains why a single national rainfall figure describes nowhere in particular — the range within the island is larger than the difference between many countries.
Hurricane exposure
- The island sits at the southern margin of the main hurricane belt
- It is affected less frequently than islands further north
- It is not exempt, and has experienced severe events
- The season runs roughly June to November
- Lower frequency raises complacency risk, which is itself a hazard
The last point deserves emphasis in a reference context. A place struck rarely accumulates building stock, habits and institutional memory calibrated to a quiet period, which is precisely why an eventual severe event causes disproportionate damage.
Reading climate data
- Note the station location, given the rainfall gradient
- Note the averaging period, since climate normals are defined over decades
- Distinguish averages from variability, which matters more for water and agriculture
- Treat single-year figures as weather, not climate
- Check whether storm statistics count all storms or only landfalls
Point one is essential here. A rainfall figure from a coastal station and one from an interior station describe the same island and different climates, and citing one as the national figure is misleading either way.
Frequently asked questions
What defines the seasons here?
Rainfall rather than temperature, driven by the seasonal migration of the tropical rain belt over or away from the region.
Why does rainfall vary so much across a small island?
Topography. Moist air forced up over the interior rains on the highlands, leaving the leeward coast in rain shadow — a several-fold difference.
Is being at the southern margin of the hurricane belt an advantage?
Partly. Lower frequency also builds complacency in building stock and habits, which is why an eventual severe event does disproportionate damage.
Why does the weather station location matter?
Because coastal and interior stations describe different climates on the same island, so neither is a national figure.
