Tropical Update: 4 Tropical Waves, The ITCZ To Bring Adverse Weather To T&T

Tropical Update Overview:
Tropical Wave 09 – This active tropical wave is producing showers and thunderstorms east of Trinidad and Tobago, forecast to bring heavy rainfall to T&T on Wednesday, beginning a multi-day heavy rainfall event as it brings the ITCZ across the islands. It has a low chance of tropical cyclone formation over the next 48 hours. An Adverse Weather Alert will go into effect 5:00 AM Wednesday through 4:00 PM Thursday.
Tropical Wave 10 – Another active tropical wave is forecast to move across Trinidad and Tobago on Thursday, bringing another round of showers and thunderstorms to the region, also keeping the ITCZ across the islands.

Key messages for the next 5 days as four tropical waves and the ITCZ forecast to affect the region, bringing periods of inclement weather to Trinidad and Tobago.

Tropical Wave 11 – A fast-moving tropical wave is forecast to move across Trinidad and Tobago, ahead of a significant surge of Saharan Dust, arriving across T&T late Friday into Saturday. A surge in trade winds will bring gusty winds and agitated seas to the region.
Tropical Wave 12 – A new tropical wave has entered the Atlantic Ocean, forecast to bring more moisture, showers, and thunderstorms to T&T later this weekend into next Monday, limiting Saharan Dust concentration.
The Intertropical Convergence Zone – With back-to-back low-latitude tropical waves, the ITCZ will remain across the region beginning Wednesday through next Monday. Based on research, the ITCZ in the Tropical Atlantic has its strongest activity occurring between 12:00 AM and 6:00 AM local time, with another peak between 12:00 PM to 3:00 PM. This is when we expect peak shower and thunderstorm activity to occur.

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 continue to monitor Tropical Wave 09 for the low chance of tropical development but conditions are unfavorable. Regardless of development, locally heavy rainfall and gusty winds are forecast beginning Wednesday through Monday with a lull in activity on Friday. 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 35-55 KM/H, occasionally in excess of 60 KM/H, and frequent lightning. As the week progress, riverine flooding, landslides, and rough seas are 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 09

Tropical Wave 09 is analyzed along 58W, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms east of Trinidad and Tobago. (Weathernerds)
Tropical Wave 09 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 8:00 PM Tropical Update, the ninth 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 15-20 knots (28-37 KM/H).

We’ve been keeping a close eye on this wave for the potential for tropical cyclone development over the last few days. Today, the National Hurricane Center tagged this wave, giving it a low (10%) chance for tropical cyclone formation over the next 48 hours to 5 days as it moves westward.

From their 8:00 PM Tropical Weather Outlook, “Showers and thunderstorms located a few hundred miles east and southeast of Trinidad and Tobago are associated with a westward-moving tropical wave. Upper-level winds are becoming less conducive for development, and the system is forecast to interact with the landmass of South America tonight and Wednesday. Regardless of development, this system could produce gusty winds and heavy rainfall over Trinidad and Tobago and the northeastern coastal sections of Venezuela during the next day or two.

The National Hurricane Center's Tropical Weather Outlook for Tropical Wave 09
The National Hurricane Center’s Tropical Weather Outlook for Tropical Wave 09

Model support has decreased for development, with no top global model supporting development, and only less than 5% of ensemble models from the EMCWF (EPS) bring this disturbance to tropical depression strength.

Again, regardless of development, gusty winds and heavy rainfall are expected across Trinidad and Tobago on Wednesday due to this wave and the Intertropical Convergence Zone moving across the region.

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 strong across the area, between 25-40 knots. While upper-level winds are unfavorable for development, an upper-level trough is optimally positioned for enhancement of convection. Hence, there is a high to very high chance of heavy to violent showers and strong thunderstorms through Wednesday.

Widespread heavy rainfall is forecast, with strong thunderstorm activity producing gusty winds, street/flash flooding, and other severe weather impacts. This will be the beginning of a multi-day heavy rainfall event across Because of this, an Adverse Weather Alert (Yellow Level) goes into effect at 5:00 AM Wednesday through 4:00 PM Thursday.

Guidance from the top global models is in agreement with this possible outcome. See below for details.

Tropical Wave 10

Tropical Waves 09 (at 58W) and 10 (at 48W) in the Eastern Atlantic Ocean, embedded within the ITCZ. (Weathernerds)
Tropical Waves 09 (at 58W) and 10 (at 48W) in the Eastern Atlantic Ocean, embedded within the ITCZ. (Weathernerds)

As of the 8:00 PM Tropical Update, further east, the axis of Tropical Wave 10 is approximately along 48W from 13N southward, moving west at 15-20 knots (28-37 KM/H).

Model guidance continues to show this wave moving across the region on Thursday, keeping the Intertropical Convergence Zone across Trinidad and Tobago.

Based on research, the ITCZ in the Tropical Atlantic has its strongest activity occurring between 12:00 AM and 6:00 AM local time, with another peak during the Northern Hemisphere summer months between 12:00 PM to 3:00 PM. Minimum activity occurs between 5:00 PM to 8:00 PM. This is when we expect peak shower and thunderstorm activity to occur.

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 Waves 09 (at 58W) and 10 (at 48W), and 11 (32W to 36W) in the Eastern Atlantic Ocean, embedded within the ITCZ. (Weathernerds)
Tropical Waves 09 (at 58W) and 10 (at 48W), and 11 (32W to 36W) in the Eastern Atlantic Ocean, embedded within the ITCZ. (Weathernerds)

As of the 8:00 PM Tropical Update, further east, the axis of Tropical Wave 11 is approximately along 32W to 36W from 20N southward, moving west at 20 knots (37 KM/H). This tropical wave is associated with a trade wind surge.

Trade wind surges are increases in the surface wind speed which come from the general direction of the trade winds (easterly winds) and are caused by any feature which causes a tightening in the pressure gradient. This could include the strengthening of a nearby high-pressure system or the passage of a low-pressure system.

A trade wind surge can cause an increase in wind convergence along the ITCZ, which generally results in increased convection and the development of clouds and thunderstorms.

This tropical wave will sustain rainfall, albeit more isolated to scattered compared to the previous two days of widespread activity, on Friday into Saturday. However, this trade wind surge will precede Tropical Wave 12 Sunday into Monday, with heavy rainfall mainly on Saturday into Sunday.

See below for details.

Tropical Wave 12

Tropical Wave 11 has just entered the Eastern Atlantic Ocean, presently along 18/19W. (Weathernerds)
Tropical Wave 12 has just entered the Eastern Atlantic Ocean, presently along 15W. (Weathernerds)

As of the 8:00 PM Tropical Update, the axis of Tropical Wave 12, newly emerged in the Atlantic, is approximately along is along 15W from 13N southward, moving westward 10-15 knots (18.5-28 KM/H). This wave is forecast to increase in forward speed, moving across Trinidad and Tobago on Sunday through Monday.

This wave may return the ITCZ across T&T through Monday, when a significant surge of Saharan Dust will move in on Tuesday, pushing the ITCZ southward and causing the drying of the atmosphere.

As mentioned above, this wave will coincide with a surge in trade winds on Sunday through next week, with gusty winds up to 60 KM/H likely and sustained winds up to 45 KM/H.

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, Tropical Wave 11, and Tropical Wave 12 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-Monday with a lull in activity on Friday.

What does all of this mean for Trinidad and Tobago?

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 after midnight 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 60 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 2.5 meters in open waters and near 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 be day two of widespread heavy rainfall.

Gusty winds, in excess of 60 KM/H, street flooding, and flash flooding are possible in heavy to violent showers and thunderstorms. Seas to remain moderate, with waves up to 2.5 meters in open waters and near 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 of heavy rainfall, the possibility of riverine flooding will be increasing.


Friday: As the axis of Tropical Wave 10 moves west, a brief surge of Saharan Dust will move in across the islands, with higher concentrations across Tobago. However, as the ITCZ shifts southward slightly, isolated thunderstorms and isolated to scattered showers are forecast to favor Trinidad throughout the day.

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 2.5 meters in open waters and near 1.0 meter in sheltered areas but may become choppy during heavy showers and thunderstorms. With heavy rainfall possible, landslides are likely. The possibility of riverine flooding will be elevated, based on overall rainfall totals from the prior days.



Saturday: The axis of Tropical Wave 11 will be moving across Trinidad and Tobago, as well as the Windward Islands, overnight Friday Saturday, bringing the ITCZ across T&T. Showers and isolated thunderstorms are forecast to occur after midnight through the afternoon, gradually settling by 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 2.5 meters in open waters and near 1.0 meter in sheltered areas but may become choppy during heavy showers and thunderstorms. With heavy rainfall possible, landslides are likely. The possibility of riverine flooding will be elevated, based on overall rainfall totals from the prior days.


Sunday: A high-pressure system will briefly regain dominance, with dense Saharan Dust remaining north of Trinidad, mostly affecting Tobago. Across Trinidad, the ITCZ and lingering moisture will continue to fuel showers and thunderstorms across the island, interrupting partly to mostly cloudy and hazy skies. Mostly settled and hazy skies are forecast across Tobago, with the odd isolated shower. By the late night, the axis of Tropical Wave 12 will be moving across Trinidad and Tobago.

Gusty winds, in excess of 60 KM/H, street flooding, and flash flooding are possible in heavy to violent showers and thunderstorms. Seas to remain moderate, with waves up to 2.5 meters, occasionally up to 3.0 meters in open waters and near 1.0 meter in sheltered areas but may become choppy during heavy showers and thunderstorms. With heavy rainfall possible, landslides are likely. The possibility of riverine flooding will be elevated, based on overall rainfall totals from the prior days.


Monday: The axis of Tropical Wave 12 is forecast to move across Trinidad and Tobago on Monday, dragging the ITCZ across the islands. Periods of showers and thunderstorms are forecast after midnight throughout the day, with a high chance of thunderstorms. Conditions are forecast to settle by the evening with a dense surge of Saharan Dust moving across the islands by nightfall.

Gusty winds, in excess of 60 KM/H, street flooding, and flash flooding are possible in heavy to violent showers and thunderstorms. Seas to become rough, with waves up to 3.0 meters in open waters and near 1.0 meter in sheltered areas but may become choppy during heavy showers and thunderstorms. With heavy rainfall possible, 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.

Winds: Sustained surface winds between 35 KM/H and 50 KM/H with gusts up to and in excess of 60 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 60 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

Wednesday-Thursday: Daily rainfall accumulations are forecast to be between 20-50 millimeters, with isolated totals between 75-100 millimeters, favoring Eastern and Southern halves of Trinidad, with similar possible totals across isolated Western Trinidad.

Friday-Saturday: Less than 15 millimeters across both islands, with isolated totals up to 25 millimeters, particularly across Trinidad in areas that experience heavy downpours and localized thunderstorms.

Sunday-Monday: Less than 20 millimeters across both islands, with isolated totals up to 40 millimeters, particularly across Trinidad in areas that experience heavy downpours and localized thunderstorms and across Eastern Trinidad.

Overall rainfall totals, through the next 6 days are forecast to be widespread 50-100 millimeters of rainfall with isolated totals up to 175 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 Friday through Monday, 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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