Tropical Update: 4 Tropical Waves, ITCZ To Move Across T&T Over Next Week

Tropical Update Overview:
Tropical Wave 08 – This tropical wave is forecast to move across T&T overnight Sunday into Monday, with showers and isolated thunderstorms possible through Monday afternoon. See below for details.
Tropical Wave 09 & 10 – Back-to-back tropical waves are forecast to move across T&T Wednesday into Thursday, in conjunction with the ITCZ, bringing locally heavy rainfall and the threat of severe weather to the islands.
Tropical Wave 11 – A fast-moving tropical wave is forecast to move across the Atlantic, ahead of a significant surge of Saharan Dust, arriving across T&T Friday into Saturday.
The Intertropical Convergence Zone

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.
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&TWe’re monitoring Tropical Wave 09 for the low chance of tropical development but conditions remain unfavorable. Regardless of development, locally heavy rainfall and gusty winds are forecast beginning Wednesday through Saturday. These tropical waves are also forecast to bring the Intertropical Convergence Zone across the islands for the first time for 2020. Beginning after midnight, into 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 58W, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms east of Trinidad and Tobago. (Weathernerds)
Tropical Wave 08 is analyzed along 58W, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms east of Trinidad and Tobago. (Weathernerds)

As of the 7:00 PM Tropical Update, the eighth tropical wave for the 2020 Atlantic Hurricane Season is located along 58W, from 13N southward based on our analysis.

The wave axis is moving westward around 10-15 knots (18.5-28 KM/H).

Scattered moderate isolated strong convection is seen from 07N-11N within 120 nm ahead and within 360 nautical miles behind the wave axis.

An enhancement of showers is likely over the southern Windward Islands tonight into early Monday.

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 to moderate 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 brief intervals of showers and the odd isolated thunderstorm, favoring overnight hours. 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 58W), 09 (at 49W), and 10 (35W to 39W) in the Eastern Atlantic Ocean, embedded within the ITCZ. (Weathernerds)
Tropical Waves 08 (at 58W), 09 (at 49W), and 10 (35W to 39W) in the Eastern Atlantic Ocean, embedded within the ITCZ. (Weathernerds)

As of the 7:00 PM Tropical Update, the axis of Tropical Wave 09 is approximately along is along 49W from 12N southward, moving westward 10-15 knots (18-28 KM/H). Scattered moderate convection is observed on both sides of the axis, embedded within the ITCZ.

Tropical Wave 09 is forecast to move across Trinidad and Tobago beginning late Tuesday through Wednesday. Model guidance continues to show that this tropical wave is also forecast to bring the ITCZ across T&T beginning after midnight Tuesday into Wednesday. In addition, the European model, which is considered one of the top global weather models, indicate the potential for tropical cyclone formation.

The European (EMCWF) Ensemble (EPS) 12Z June 14th, 2020 runs showing a 60% probability of tropical-depression-winds from Tropical Wave 09. (Weathermodels)
The European (EMCWF) Ensemble (EPS) 12Z June 14th, 2020 runs showing a 60% probability of tropical-depression-winds from Tropical Wave 09. (Weathermodels)

The EMCWF ensembles, not the operational run, show 60% of the ensemble models developing Tropical Wave 09 into a tropical depression. The operational EMCWF, as well as all other global models, keep this as a strong tropical wave, with gusty winds in excess of 65 KM/H on Wednesday, as it moves across the islands. This wave is not tagged for development by the NHC at this time.

Further east, the axis of Tropical Wave 10 is approximately along 35W to 39W from 20N southward, moving at 10-15 knots (18-28 KM/H).

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 Thursday. 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 Southern and Eastern Trinidad but widespread heavy rainfall is forecast. Guidance from the top global models is in agreement with this possible outcome.

See below for details.

Tropical Wave 11

Tropical Wave 11 has just entered the Eastern Atlantic Ocean, presently along 18/19W. (Weathernerds)
Tropical Wave 11 has just entered the Eastern Atlantic Ocean, presently along 18/19W. (Weathernerds)

As of the 7:00 PM Tropical Update, the axis of Tropical Wave 11, newly emerged in the Atlantic, is approximately along is along 18/19W from 13N southward, moving westward 15 knots (28 KM/H). This wave is forecast to increase in forward speed, moving across Trinidad and Tobago on Friday.

The U.S. Model Ensembles (GEFS) showing Tropical Wave 11 moving quickly across the Atlantic, to T&T within 120 hours (5 days)
The U.S. Model Ensembles (GEFS) showing Tropical Wave 11 moving quickly across the Atlantic, to T&T within 120 hours (5 days)

Continuing from the anticipated two days of heavy rainfall, this wave will keep the ITCZ across T&T through Saturday, when a significant surge of Saharan Dust will move in, pushing the ITCZ southward and causing the drying of the atmosphere.

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. 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, Tropical Wave 10, and now Tropical Wave 11 are forecast to drag the feature and maintain its position across the islands through the week.

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

What does all of this mean for Trinidad and Tobago?

The remainder of Sunday: Partly to mostly cloudy skies interrupted by isolated showers. Tropical Wave 08 is forecast to move across the islands overnight into tomorrow (Monday). Hence, isolated showers are forecast to develop by the late night, with isolated thunderstorms possible after midnight.

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 2.0 meters in open waters and below 1.0 meter 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, as well as after midnight, across Trinidad. Thunderstorm chances are 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 high-pressure system will briefly dominate conditions on Tuesday, with a surge of Saharan Dust moving in overnight Monday and throughout Tuesday. Shower and thunderstorm chances remain low, with only brisk and highly isolated showers possible. After nightfall, particularly after midnight into Wednesday, shower and thunderstorm chances increase as both the ITCZ and Tropical Wave 09 approaches the islands.

No significant impacts forecast on Tuesday until the late night into Wednesday. Air quality may be reduced to moderate levels due to Saharan Dust. Improvement is forecast after midnight. 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.


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. Based on present model guidance, gusty winds up to and in excess of 65 KM/H are possible.

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. This is forecast to be day one of widespread heavy rainfall.


Thursday: The axis of Tropical Wave 09 will move west, with the ITCZ remaining across Trinidad and Tobago. The axis of Tropical Wave 10 will move across Trinidad. 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, day two of widespread heavy rainfall.

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: The axis of Tropical Wave 11 will be moving across Trinidad and Tobago, as well as the Windward Islands on Friday into Saturday, keeping the ITCZ across T&T. On both days, 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. On Saturday, by the late evening, a significant surge of Saharan Dust is forecast to move into the region.

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 65 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. On Wednesday, gusts in excess of 65 KM/H are possible.

With wind gusts in excess of 65 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

Monday: Less than 15 millimeters across Tobago. Less than 20 millimeters across Trinidad with isolated totals exceeding 25 millimeters.

Tuesday: Less than 5 millimeters across both islands.

Wednesday-Thursday: 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.

On Friday through Saturday: Daily rainfall accumulations are forecast to be up to 25 millimeters with isolated totals up to 40 millimeters across both islands. Heavier totals likely across eastern parts of the islands.

Overall rainfall totals, through the next 7 days are forecast to be widespread 50-75 millimeters of rainfall with isolated totals between 100-200 millimeters.

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 by the end of the week.

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 through Tuesday and Friday through Saturday, 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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