Forecast: ITCZ, Tropical Wave 17 Affecting T&T Ahead Of Significant Saharan Dust Surge

As forecast, the Intertropical Convergence Zone and back-to-back tropical waves affected Trinidad and Tobago over the last 72 hours. Periodic rain, showers, and thunderstorms are forecast to continue through early Monday, with a dense plume of Saharan Dust moving across the Eastern Caribbean later today (Sunday).

What you need to know

Saharan Dust: A significant surge of dust is forecast to arrive by late Sunday (today) and linger through the week, with brief improvement forecast by late Tuesday into late Wednesday and again by the weekend.
Rainfall: Periodic light to moderate rain, isolated heavy to violent showers, and isolated thunderstorms are forecast across mainly Trinidad on Sunday, with isolated activity through the remainder of the week.
Hazards: The main hazards over the next 24 hours, when most of the impactful weather is forecast, are gusty winds up to and in excess of 45 KM/H accompanying heavy showers or thunderstorms, as well as localized street/flash flooding favoring eastern and southern Trinidad. The chances for riverine flooding remain low at this time. Lightning will accompany thunderstorms.
Alerts/Watches/Warnings: There are no alerts, watches, or warnings in effect for T&T from the Trinidad and Tobago Meteorological Service at this time. There are also no tropical storm or hurricane watches or warnings in effect for T&T.

The Forecast

Sunday – Tropical Wave 17 & The ITCZ

Sunday – Tropical Wave 17 & The ITCZ
7 10 0 1
Variably cloudy day with scattered showers and thunderstorms forecast from the early morning through the early afternoon. Overall heavier rainfall to favor southern and eastern halves of Trinidad. Increasingly hazy conditions will join cloudy skies by the late afternoon into the night, interrupted by light to moderate rain and the occasional heavier shower. After nightfall, there is a low chance of an isolated thunderstorm, favoring southern and southeastern Trinidad. Gusty winds, street/flash flooding possible.
Variably cloudy day with scattered showers and thunderstorms forecast from the early morning through the early afternoon. Overall heavier rainfall to favor southern and eastern halves of Trinidad. Increasingly hazy conditions will join cloudy skies by the late afternoon into the night, interrupted by light to moderate rain and the occasional heavier shower. After nightfall, there is a low chance of an isolated thunderstorm, favoring southern and southeastern Trinidad. Gusty winds, street/flash flooding possible.
7/10
Thunderstorm Chances
High

Monday – Saharan Dust Dominates

Monday – Saharan Dust Dominates
2 10 0 1
Partly to mostly cloudy, hazy and breezy with brief showers favoring Trinidad. There is a low to very low chance of an isolated thunderstorm favoring southern Trinidad. Mostly hazy night.
Partly to mostly cloudy, hazy and breezy with brief showers favoring Trinidad. There is a low to very low chance of an isolated thunderstorm favoring southern Trinidad. Mostly hazy night.
2/10
Thunderstorm Chances
Very Low – Low

Tuesday

Tuesday
1 10 0 1
Mostly hazy, breezy and partly cloudy conditions, interrupted the odd, brisk isolated shower favoring southern and eastern Trinidad, mainly during the predawn and early afternoon hours. Partly cloudy and settled night.
Mostly hazy, breezy and partly cloudy conditions, interrupted the odd, brisk isolated shower favoring southern and eastern Trinidad, mainly during the predawn and early afternoon hours. Partly cloudy and settled night.
1/10
Thunderstorm Chances
Very Low

Wednesday

Wednesday
1 10 0 1
Mostly hazy, breezy and partly cloudy conditions, interrupted the odd, brisk isolated shower favoring eastern Trinidad. Partly cloudy and settled night.
Mostly hazy, breezy and partly cloudy conditions, interrupted the odd, brisk isolated shower favoring eastern Trinidad. Partly cloudy and settled night.
1/10
Thunderstorm Chances
Very Low

Thursday – More Saharan Dust

Thursday – More Saharan Dust
1 10 0 1
Mostly hazy, breezy and partly cloudy conditions, interrupted the odd, brisk isolated shower favoring eastern Trinidad. Partly cloudy and settled night.
Mostly hazy, breezy and partly cloudy conditions, interrupted the odd, brisk isolated shower favoring eastern Trinidad. Partly cloudy and settled night.
1/10
Thunderstorm Chances
Very Low

Marine: Through Thursday, seas are forecast to be moderate with waves in open waters up to 2.0 meters, occasionally exceeding 2.0 meters on Sunday and Monday. In sheltered areas, waves are forecast to be near or below 1.0 meter, becoming choppy associated with increased low-level winds and rainfall activity on Sunday into Monday.

Temperatures

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

On Sunday, maximum highs across the country are forecast to be below 30.0°C in Trinidad and Tobago. In urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas, the maximum high temperatures could exceed 30.0°C.

From Monday, maximum highs across the country are forecast to be generally up to 32.0°C in Trinidad and Tobago. In urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas, the maximum high temperatures could exceed 33.0°C.

Forecast Impacts

Flooding

Flooding
7 10 0 1
Over the next five days, between 25 and 75 millimeters of rainfall is forecast across most of the country. Lower rainfall totals are forecast across northwestern/west-central areas of Trinidad while higher totals are forecast across the eastern and southern halves of Trinidad, where isolated rainfall totals up to 100 millimeters are forecast. In highly isolated areas, overall five-day rainfall totals could exceed 100 millimeters.
Over the next five days, between 25 and 75 millimeters of rainfall is forecast across most of the country. Lower rainfall totals are forecast across northwestern/west-central areas of Trinidad while higher totals are forecast across the eastern and southern halves of Trinidad, where isolated rainfall totals up to 100 millimeters are forecast. In highly isolated areas, overall five-day rainfall totals could exceed 100 millimeters.
7/10
Likelihood
High

There is a high chance of street and flash flooding, mainly on Sunday, and across central. southern, and eastern Trinidad. Chances for riverine flooding remain low as major rivers across the country are well within their banks.

Forecast Rainfall Totals

  • Sunday: Across northwestern and north-central Trinidad, as well as most of Tobago, less than 15 millimeters of rainfall is forecast with isolated higher totals where heavy showers or isolated thunderstorms occur. Across the southern and eastern halves of Trinidad, between 25 and 50 millimeters of rainfall, with isolated higher totals up to 125 millimeters.
  • Monday: Less than 5 millimeters across the country, with isolated totals up to 10 millimeters across eastern and southern areas of Trinidad.
  • Tuesday: Less than 5 millimeters across the country, with isolated totals up to 10 millimeters mainly across eastern and southern areas of Trinidad.
  • Wednesday: Between 5 and 15 millimeters across the country with rainfall totals trending higher across southern and eastern areas of Trinidad.
  • Thursday: Less than 5 millimeters across the country, mainly across eastern areas of Trinidad and across Tobago.

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.

Strong Thunderstorms

Strong Thunderstorms
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Wind shear is forecast to be moderate to strong, with varying degrees of dryness throughout the atmosphere. In addition, strong low-level winds are forecast to keep convection moving briskly. However, there is a favorable upper-level pattern in place that is forecast to enhance showers and thunderstorms. Taking a combination of these factors into consideration, the chances of strong thunderstorms developing are low.
Wind shear is forecast to be moderate to strong, with varying degrees of dryness throughout the atmosphere. In addition, strong low-level winds are forecast to keep convection moving briskly. However, there is a favorable upper-level pattern in place that is forecast to enhance showers and thunderstorms. Taking a combination of these factors into consideration, the chances of strong thunderstorms developing are low.
3/10
Likelihood
Low

Funnel cloud development is unlikely due to moderate to strong low-level winds. If a funnel cloud touches down on a body of water, it becomes a waterspout; if it touches down on land, it becomes a tornado.

While frequent cloud-to-ground lightning isn’t likely, lightning is expected in thunderstorm activity.

Gusty Winds

Gusty Winds
7 10 0 1
Low-level winds across the region are forecast remain elevated through Monday. Strong gusts could accompany heavier thunderstorms or shower activity. Sustained winds up to 35 KM/H are forecast, with gusts up to 45 KM/H likely. Stronger winds and gusts, in excess of 45 KM/H are possible, accompanying heavy shower or thunderstorm activity on Sunday.
Low-level winds across the region are forecast remain elevated through Monday. Strong gusts could accompany heavier thunderstorms or shower activity. Sustained winds up to 35 KM/H are forecast, with gusts up to 45 KM/H likely. Stronger winds and gusts, in excess of 45 KM/H are possible, accompanying heavy shower or thunderstorm activity on Sunday.
7/10
Likelihood
High

With wind gusts up to and 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.

Other Hazards

Saharan Dust will remain across the region through the forecast period, reducing air quality and affecting visibility.

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.

Isolated to scattered rainfall is forecast on Sunday, with isolated rainfall from Monday.

Forecast Discussion

8:00 PM Sunday Tropical Weather Outlook from the National Hurricane Center
8:00 PM Sunday Tropical Weather Outlook from the National Hurricane Center

Tropical Waves East of T&T: Based on the Tropical Analysis and Forecast Branch’s 00Z surface analysis on July 10th, 2022, as well as the latest satellite and model guidance:

  • The 17th tropical wave for 2022 (TW17) is along 56°W, south of 18°N, moving west at 20 knots (37 KM/H). Isolated moderate to strong convection as been noted where the wave interacts with the Intertropical Convergence Zone, mainly between 7°N to 10°N and 50°N to 60°N. This wave is forecast to move across T&T early Sunday.
  • The 18th tropical wave for 2022 (TW18) is along 26°W, south of 18°N, moving west at 10-15 knots (18-27 KM/H). This wave is forecast to move across Trinidad and Tobago on Friday into Saturday, July 15th to 16th, 2022. There are some weak showers where the wave meets the ITCZ, while dense Saharan Dust limits convection elsewhere.

As of early Sunday morning, marginally favorable upper-level conditions are in place across Trinidad and Tobago, resulting from a stationary upper-level low anchored in the central Caribbean Sea. This upper-level low is creating favorable upper-level divergence across the Lesser Antilles and this pattern is forecast to hold through Tuesday, enhancing any shower or thunderstorm that develops.

At the lower levels, high atmospheric moisture and instability associated with the Intertropical Convergence Zone and Tropical Wave 17 is moving across Trinidad and Tobago, supporting broad cloudiness with rain, showers, and thunderstorms predominantly affecting southern and eastern areas of Trinidad. The ITCZ remains just south of the country but may drift across T&T on Sunday. Strong to very strong wind shear from the west to southwest continues to keep shower and thunderstorm activity brief.

A significant surge of Saharan Dust is forecast to trail Tropical Wave 17, beginning to move across the Eastern Caribbean by Sunday afternoon. This dust surge will be accompanied by a surface to a mid-level ridge that is forecast to establish across the Lesser Antilles through the week. While low-level cloud patches may bring brief showers through the week, enhanced by the upper-level low-pressure system through Tuesday, Saharan Dust is forecast to keep low to mid-levels of the atmosphere fairly dry. This setup is forecast to lead to partly cloudy and hazy skies, with the occasional brief shower, as reflected in the forecast through the week.

By late Thursday into Friday, the approach of Tropical Wave 18 is forecast to bring the Intertropical Convergence Zone back to Trinidad and Tobago, with high atmospheric moisture and instability set to affect the country through the weekend.

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