Forecast: Sunny Skies Mixed With Isolated Showers, Thunderstorms This Week

Key Messages:
— Tropical Wave 55 (a tropical disturbance also called Invest 93L) and the Intertropical Convergence Zone are forecast to bring rainfall to the Windward Islands over the next five days, with heavier rain remaining north and east of T&T.
— Generally, street and flash flooding will favor Northern Trinidad and across Tobago. By Wednesday, the flooding threat will be elevated. Wind gusts in excess of 45 KM/H are possible.
Lightning will accompany thunderstorms. Funnel clouds and waterspouts are possible, mainly Tuesday through Wednesday and on Friday.
— There are no alerts, watches, or warnings in effect from the Trinidad and Tobago Meteorological Service for T&T at this time.

The Forecast

Moisture trailing Tropical Wave 54 and ahead of Tropical Wave 55 moving across and nearing the region respectively. (SSEC/CIMSS/UW-Madison)
Moisture trailing Tropical Wave 54 and ahead of Tropical Wave 55 moving across and nearing the region respectively. (SSEC/CIMSS/UW-Madison)

Monday: Isolated to scattered showers and isolated thunderstorms are forecast during the early morning, favoring eastern and southern Trinidad. By the mid to late morning, isolated showers and thunderstorms are forecast to spread across Trinidad, interrupting partly to mostly cloudy periods and continue through the afternoon. Isolated showers are possible across Tobago throughout the day. Conditions are forecast to settle into the evening, with a resurgence of showers and thunderstorms from the east overnight across both islands.

Tuesday: Generally partly cloudy skies across the country, interrupted by isolated showers and thunderstorms favoring the late morning through the afternoon across western areas of the country. Mostly settled conditions are forecast by the evening and night, barring the odd shower.

Wednesday: After a mostly settled night, showers and thunderstorms are forecast to develop near dawn, favoring eastern Trinidad and Tobago initially, moving west across the country. Scattered showers and thunderstorms are forecast to continue through the day across both islands and continue into the night. Overnight thunderstorms are forecast to favor offshore areas.

Thursday: Brisk isolated showers and thunderstorms are possible overnight, favoring Trinidad’s eastern and southern areas, giving way to an initially partly to a mostly cloudy and hazy day. By the late morning through the afternoon, isolated heavy showers and isolated thunderstorms are forecast to move across the country, and conditions are forecast to settle into the evening.

Friday: A partly cloudy day interrupted by late morning through afternoon showers and isolated thunderstorms favoring western and hilly areas of Trinidad, with mostly sunny conditions across Tobago.

Scattered showers and thunderstorms east of the Lesser Antilles on Monday morning (Weathernerds.org)
Scattered showers and thunderstorms east of the Lesser Antilles on Monday morning (Weathernerds.org)

Marine: Seas are forecast to be moderate in open waters with waves up to 2.0 meters. Seas are forecast to be near or below 1.0 meter in sheltered areas, becoming choppy during heavier showers or thunderstorms. Larger waves are possible in nearshore areas due to long-period swells between 11 to 15 seconds from the north, peaking on Wednesday.

Temperatures

Through the forecast period, the minimum low in Trinidad is forecast to be between 23.0°C and 26.0°C. In Tobago, the minimum low is forecast to be between 24.0°C and 27.0°C.

Maximum highs across the country are forecast to be generally up to 33.0°C in Trinidad and 32.0°C in Tobago. However, with increased cloud cover, particularly on Wednesday, maximum highs are forecast to be relatively cooler.

In urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas, the maximum high temperatures could exceed 36.0°C on days with sunny mornings.

Forecast Impacts

Forecast impacts due to Tropical Wave 55 and the ITCZ over the next five days.

On Tuesday, an active tropical wave, Tropical Wave 55 (also called Invest 93L as the National Hurricane Center monitors it for development), is forecast to move north of Trinidad and Tobago.

While development chances of this system remain low, atmospheric conditions will be favorable for shower and thunderstorm development across Trinidad, Tobago, and the remainder of the Lesser Antilles. Localized street/flash flooding, damaging gusty winds (in excess of 45 KM/H), and other severe thunderstorm impacts such as frequent lightning, funnel cloud, or waterspout development is possible, with funnel clouds/waterspouts mainly possible on Tuesday into Wednesday and on Friday.

Winds

Sustained surface winds are forecast to be between 15 to 35 KM/H. In heavy to violent shower and thunderstorm activity, gusts up to and in excess of 45 KM/H are possible. With wind gusts in excess of 45 KM/H, whole trees are expected to be in motion, and there may be some inconvenience when walking against the wind gusts. Light outdoor objects may topple or become airborne such as garbage cans, potted plants, loose galvanize or construction material, and other outdoor furniture. Tents may jump. Older/weaker trees may fall, bringing down utility poles and lines.

Rainfall

Scattered showers and thunderstorms producing heavy rainfall are mainly forecast to remain north of the country.

Higher rainfall totals are forecast to favor eastern areas of both Trinidad and Tobago. Generally, less than 25 millimeters are forecast across the country, with isolated totals up to 75 millimeters. Isolated high totals are also possible along the western coastal areas of Trinidad.

  • Monday: Less than 10 millimeters across the country with isolated totals up to 20 millimeters favoring the southern half of Trinidad and areas where isolated heavy showers or thunderstorms occur.
  • Tuesday: Less than 5 millimeters across the country with isolated totals up to 15 millimeters in areas where isolated heavy showers or thunderstorms occur, mainly across Trinidad.
  • Wednesday: This is forecast to be the wettest day of the week. Up to 25 millimeters across the country, trending wetter across the eastern halves of both islands. Isolated totals in excess of 25 millimeters are possible.
  • Thursday: Up to 15 millimeters across the country, trending wetter across the southern and eastern halves Trinidad.
  • Friday: Less than 5 millimeters across the country with isolated totals up to 15 millimeters in areas where isolated heavy showers or thunderstorms occur, mainly across Trinidad.

Street flooding or flash flooding is possible over the next five days with medium chances, mainly on Wednesday. Chances for riverine flooding remain very low at this time, as model guidance suggests heavier rainfall remains north of the country.

Putting the rainfall forecast into context, rainfall rates in excess of 50 millimeters per hour or areas that receive in excess of 25 millimeters within an hour tend to trigger street flooding across the country or flash flooding in northern Trinidad. For riverine flooding to occur, a large area of the country (not just in highly localized areas of western coastal Trinidad) would have to record upwards of 75 millimeters within 24 hours, and rainfall would have to fall across major rivers’ catchment areas.

Other Adverse Weather Impacts

Lightning: Lightning is possible in thunderstorm activity. Lightning can cause power outages, voltage dips, damage to life and property, particularly during cloud-to-ground lightning strikes. Dangerous, frequent lightning is expected on Friday and Saturday.

Landslides: Landslides and fallen trees are possible, particularly along the Northern Range.

Severe Thunderstorms: The potential for severe thunderstorms, funnel clouds, and waterspouts remain low. Funnel clouds and waterspouts are possible mainly on Tuesday into Wednesday and on Friday. If funnel clouds touchdown or waterspouts encounter land, weak tornadoes can form.

Why I May Not/Will Not See Rainfall?

A frequent complaint is the forecast is wrong because I didn’t experience any rainfall. Scattered showers mean that you, individually, may experience some showers intermittently throughout the day, and there is a higher chance for this activity than isolated activity. Widespread showers mean that nearly all persons and areas may experience rainfall.

Through the forecast period, isolated to scattered rainfall is forecast.

Forecast - Isolated, Scattered, Widespread - What do they mean?

Forecast Discussion

Surface analysis over the last few days showing the progression of Tropical Waves east of the Lesser Antilles (NHC/TAFB/NOAA)
Surface analysis over the last few days showing the progression of Tropical Waves east of the Lesser Antilles (NHC/TAFB/NOAA)

Tropical Waves: At 00Z Monday 11th October 2021, the axis of Tropical Wave 54 is along 67°W moving westward at 15 knots (27 KM/H) with scattered showers and isolated strong thunderstorms. Tropical Wave 55 is along 52°W from 16°N southward, moving west at 10 to 15 knots (18-27 KM/H) with scattered showers and isolated strong thunderstorms.

Deep-layered moisture associated with Tropical Wave 55/Invest 93L is forecast to affect the Lesser Antilles, including Trinidad and Tobago, through mid-week. Environmental conditions are not forecast to be favorable for development as the system’s core moves north of T&T.

On Monday, convergence ahead of Tropical Wave 55/Invest 93L and a marginally favorable upper-level pattern will support isolated to scattered showers and thunderstorms accompanied by gusty winds. As Tropical Wave 55 nears and moves across the region on Tuesday, an unsettled regime remains in place north of T&T, while a weak ridge holds across T&T, allowing for isolated showers interrupting sunny periods.

However, convergence trailing the passage of Tropical Wave 55/Invest 93L, light wind shear, and a favorable low and upper-level environment will support more scattered showers and thunderstorms across T&T on Wednesday.

Increased Saharan Dust will bring slightly drier conditions to lower and mid-levels of the atmosphere, limiting shower and thunderstorm development during the second half of the week and ultimately leading to drier weather.

Facebook Comments