Tropical Update: Tropical Waves, ITCZ To Bring Significant Rainfall Late Next Week

Tropical Update Overview:
Tropical Wave 08 – While this tropical wave looks impressive east of T&T presently, activity associated with this wave is forecast to dissipate at it approaches a high wind shear environment as it nears and traverses T&T late Sunday through Monday. Isolated showers, thunderstorms possible, mainly on Monday. See below for details.
Tropical Wave 09 & 10 – Back-to-back tropical waves are forecast to move across T&T late Tuesday into Thursday and late Thursday into Saturday, bringing locally heavy rainfall and the threat of severe weather to the islands.
The Intertropical Convergence Zone – This tropical wave recently emerged off the African Coast and is forecast to traverse the Lesser Antilles this upcoming weekend. However, it is too soon to tell any definitive impacts this wave may bring, particularly as a significant surge of Saharan Dust is also north of the wave axis.

Total Precipitable Water Imagery showing the Tropical Waves (analyzed by the National Hurricane Center, Weather Prediction Center, and TTWC) that exist east of Trinidad and Tobago.

Impacts to T&TNo direct tropical threats to Trinidad and Tobago are forecast over the next week but beginning Tuesday into Wednesday, into the weekend, locally heavy rainfall is forecast due to back-to-back tropical waves moving across T&T. These tropical waves are also forecast to bring the Intertropical Convergence Zone across the islands for the first time for 2020. Beginning on Wednesday, there will be an elevated threat of Street flooding, flash flooding, gusty winds generally between 35-45 KM/H, occasionally in excess of 55 KM/H, and frequent lightning. As the week progress, riverine flooding and landslides may be possible.

Before we dive into the Tropical Update, a few notes:

  • Tropical waves are a normal part of the rainy season.
  • Not every tropical wave will form into a tropical cyclone.
  • Weaker tropical waves produce more rainfall across Eastern parts of the islands with mostly cloudy conditions and a few showers across western parts of the islands.
  • Rainfall will be more isolated and intermittent with weaker tropical waves that do not have ITCZ or upper-level support.
  • Saharan Dust may weaken tropical waves.

You can read more about the weather associated with Tropical Waves, as well as what to expect as these waves move through the region below.

Tropical Wave 08

Tropical Wave 08 is analyzed along 55W, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms east of Trinidad and Tobago. (Weathernerds)
Tropical Wave 08 is analyzed along 55W, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms east of Trinidad and Tobago. (Weathernerds)

As of the 6:00 PM Tropical Update, the eighth tropical wave for the 2020 Atlantic Hurricane Season is located along 55W, from 12/13N southward based on our analysis.

The wave axis is moving westward around 10-15 knot (18.5-28 KM/H). Numerous moderate to isolated strong convection is noted from 06N-10N within 210 nautical miles W and within 300 nautical miles E of the wave axis.

An enhancement of showers is likely over the southern Windward Islands late Sunday and early Monday. The tropical wave will then move through the central Caribbean Wednesday night through Thursday night.

Presently, favorable low-level convergence and upper-level divergence are coinciding with the wave axis, as well as abundant total precipitable moisture, moving associated with the wave. Wind shear remains weak across the area, allowing for scattered convective activity.

However, as this wave approaches T&T, and traverses the island, wind shear will increase across the area keeping most showers and isolated thunderstorms offshore, with minimal activity mainly affecting Trinidad through Monday evening. No widespread heavy rainfall is forecast.

Guidance from the top global models is in agreement with this possible outcome.

See below for details.

Tropical Waves 09 & 10

Tropical Waves 08 (at 55W), 09 (at 43W), and 10 (33/34W) in the Eastern Atlantic Ocean, embedded within the ITCZ.(Weathernerds)
Tropical Waves 08 (at 55W), 09 (at 42/43W), and 10 (33/34W) in the Eastern Atlantic Ocean, embedded within the ITCZ.(Weathernerds)

As of the 6:00 PM Tropical Update, the axis of Tropical Wave 09 is approximately along is along 42/43W from 13N southward, moving westward 10-15 knots (18.5-28 KM/H). Scattered moderate convection is within 210 nautical miles, mainly east of the wave axis from 03N-10N.

Further east, the axis of Tropical Wave 10 is approximately along 29/33W from 18N southward, moving faster at 15-20 knots (28-38 KM/H). Scattered moderate convection is seen from 04N-11N within 150 nautical miles west and within 330 nautical miles east of the wave axis.

Over the last several days, models continue to show a widespread heavy rainfall event beginning late Tuesday across Trinidad and Tobago as moisture ahead of Tropical Wave 09 begins to move across Trinidad. The axis of Tropical Wave 09 is forecast to move across the area on Wednesday, with the axis of Tropical Wave 10 forecast to move across the area on Friday. Both of these waves are embedded within the Intertropical Convergence Zone, bringing deep tropical moisture and favorable convergence to T&T late this upcoming week.

While wind shear will remain moderate to strong, preventing prolonged thunderstorms and showers, favorable upper-level conditions will allow for deep convection (strong thunderstorms and showers) to develop. Heavier activity overall is forecast to favor offshore eastern Trinidad and Tobago. Widespread heavy rainfall is forecast. Guidance from the top global models is in agreement with this possible outcome.

See below for details.

Intertropical Convergence Zone

Diagram of the North and South Atlantic Subtropical Highs which produce the northeasterly and southeasterly trade winds which allow for the formation of the ITCZ. Diagram: Trinidad and Tobago Weather Center.
Diagram of the North and South Atlantic Subtropical Highs which produce the northeasterly and southeasterly trade winds which allow for the formation of the ITCZ. Diagram: Trinidad and Tobago Weather Center.

The Intertropical Convergence Zone (ITCZ) is forecast to move across Trinidad and Tobago for the first time for 2020. Tropical Wave 09 and Tropical Wave 10, both embedded within the ITCZ, is forecast to drag the feature across the islands. We’ll have more updates on this feature moving across in subsequent Tropical Updates.

Because of this, a multi-day heavy rainfall event is now forecast for Trinidad and Tobago beginning late Tuesday through late Saturday.

What does all of this mean for Trinidad and Tobago?

The remainder of Saturday: Mostly settled and hazy due to a moderate concentration of Saharan Dust present. Brisk, isolated showers possible overnight, mainly after midnight.


Sunday: Mostly sunny to partly cloudy and hazy conditions throughout the day. By the late morning through the afternoon, isolated showers are forecast to develop across Trinidad, with heavier showers favoring the southern and western areas of the island. Isolated showers also possible across Tobago, with activity remaining brisk. Thunderstorm chances remain low. Activity is forecast to settle by the evening, with cloudiness increasing due to the approaching Tropical Wave 08. Isolated showers are forecast to develop after nightfall, with isolated thunderstorms possible after midnight. No significant rainfall is expected at this time.

Gusty winds, up to 55 KM/H, and street flooding are possible in heavy to violent showers and isolated thunderstorms. Seas to remain slight to moderate, with waves up to 1.5 meters in open waters and near calm in sheltered areas but may become choppy during heavy showers and thunderstorms.


Monday: The axis of Tropical Wave 08 will be moving across Trinidad and Tobago. Showers and isolated thunderstorms are forecast to occur intermittently throughout the day, with higher chances for thunderstorms during the late morning through the afternoon, across Trinidad. Thunderstorm chances remain low to medium. Activity is forecast to settle by the evening with brisk showers favoring Trinidad. No significant rainfall is expected at this time.

Gusty winds, up to 55 KM/H, and street flooding are possible in heavy to violent showers and isolated thunderstorms. Seas to remain moderate, with waves up to 2.0 meters in open waters and below 1.0 meter in sheltered areas but may become choppy during heavy showers and thunderstorms.


Tuesday: A mostly sunny start to Tuesday is forecast, with brisk isolated showers favoring Trinidad. By the late morning, periods of showers and isolated thunderstorms are possible, with heavier activity favoring the Southern and Western halves of Trinidad. Thunderstorm chances remain medium throughout the day, becoming medium to high by nightfall. These conditions are forecast to interrupt variably cloudy skies, with heavier rainfall favoring Trinidad into the night. This is due to approaching Tropical Wave 09.

Particularly during heavy to violent showers and thunderstorms, gusty winds in excess of 55 KM/H are possible. Seas to remain moderate, with waves up to 2.0 meters in open waters and below 1.0 meter in sheltered areas but may become choppy during heavy showers and thunderstorms. Street, flash flooding, and frequent lightning are likely in heavy downpours and thunderstorms respectively. Landslides are less likely, but also possible.


Wednesday: The axis of Tropical Wave 09 is forecast to move across Trinidad and Tobago on Wednesday, dragging the ITCZ across the islands. Periods of showers and thunderstorms are forecast throughout the day, with a high chance of thunderstorms. Conditions are forecast to briefly settle by the evening, with a resurgence of showers and thunderstorms overnight.

Gusty winds, in excess of 55 KM/H, street flooding, and flash flooding are possible in heavy to violent showers and thunderstorms. Seas to remain moderate, with waves up to 2.0 meters in open waters and below 1.0 meter in sheltered areas but may become choppy during heavy showers and thunderstorms. Note that a brief long-period swell event is forecast by mid-Wednesday through early Thursday, making seas in nearshore area choppy. With heavy rainfall persisting, landslides are forecast to become increasingly likely.


Thursday: The axis of Tropical Wave 09 will move west, with the ITCZ remaining across Trinidad and Tobago. Showers and thunderstorms are forecast to begin again after midnight across both Trinidad and Tobago, with cloudy to overcast intervals persisting throughout the day and into the night. Thursday is forecast to produce the heaviest 24-hour rainfall totals.

Gusty winds, in excess of 55 KM/H, street flooding, and flash flooding are possible in heavy to violent showers and thunderstorms. Seas to remain moderate, with waves up to 2.0 meters in open waters and below 1.0 meter in sheltered areas but may become choppy during heavy showers and thunderstorms. With heavy rainfall persisting, landslides are likely. Given this will be day two to day three of heavy rainfall, the possibility of riverine flooding will be increasing.


Friday and Saturday: Overnight showers and isolated thunderstorms are forecast to occur after midnight through the afternoon, gradually settling by the late afternoon through the evening. These conditions are forecast to interrupt partly to mostly cloudy skies.

Gusty winds, in excess of 55 KM/H, street flooding, and flash flooding are possible in heavy to violent showers and thunderstorms. Seas to remain moderate, with waves up to 2.0 meters in open waters and below 1.0 meter in sheltered areas but may become choppy during heavy showers and thunderstorms. With heavy rainfall persisting, landslides are likely. The possibility of riverine flooding will be elevated, based on overall rainfall totals from the prior days.

Possible Impacts This Week

T&T's Risk Matrix for this week's inclement weather.
T&T’s Risk Matrix for this week’s inclement weather.

Winds: Sustained surface winds between 35 KM/H and 45 KM/H with gusts up to and in excess of 55 KM/H possible in heavy showers or thunderstorms across Trinidad and Tobago. There are no tropical cyclones forecast to develop, as of this tropical update.

With wind gusts in excess of 55 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.

High Wind Event Precautions
High Wind Event Precautions

Rainfall: On Monday through Tuesday, daily rainfall accumulations are forecast to be less than 5-10 millimeters, with areas that experience isolated downpours or thunderstorms, isolated totals up to 25 millimeters are possible.

On Wednesday through Friday, daily rainfall accumulations are forecast to be up to 35 millimeters, with isolated totals between 50-75 millimeters, favoring Eastern and Southern halves of Trinidad, with similar possible totals across isolated Western Trinidad.

Generally, with heavy showers and thunderstorm activity, street flooding, particularly in flood-prone areas or areas with poor drainage, is possible as well as flash flooding in areas where more prolonged heavy rainfall may occur. The possibility of riverine flooding will be elevated, based on overall rainfall totals from the prior days.

Frequent Lightning: In addition, with forecast thunderstorms, frequent lightning is likely. Lightning can cause power outages, voltage dips, damage to life and property, particularly during cloud-to-ground lightning strikes.

Why I May Not/Will Not See Constant 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.

This week, isolated to scattered activity is forecast on Monday, Tuesday and Friday, with widespread activity forecast on Wednesday and Thursday.

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

Tropical Cyclone Climatology

Tropical Cyclone Points of Origin during the month of June. Though much of the points of origin are west or north of T&T as we move through the first month of the Hurricane Season, we still need to pay attention to some of these waves and the ITCZ, which have historically brought major flooding events to T&T, hence all low-pressure systems in the Atlantic should be closely monitored, as we do in the Tropical Update.

List of names for the 2020 Atlantic Hurricane Season, which will be updated each tropical update as new systems develop.
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