Tropical Update – Three Tropical Waves, ITCZ to Affect T&T

Tropical Update Overview:
Tropical Depression Five – A tropical depression has formed in the West Atlantic, no threat to Trinidad and Tobago as it moves out to sea, just north of Bermuda.
Tropical Wave 19 & The ITCZ – A weak tropical wave is forecast to move across the Lesser Antilles late Sunday, bringing the ITCZ across Trinidad and Tobago. Severe weather is possible, beginning Sunday afternoon as heavy showers and thunderstorms begin, favoring Southern and Eastern Trinidad.
Tropical Wave 20 & The ITCZ – Another weak tropical wave is forecast to move across T&T on Monday, keeping the ITCZ across the islands, moving it north of T&T. Severe weather is likely across both islands as periods of showers and thunderstorms are forecast throughout the day on Monday.
Tropical Wave 21 & The ITCZ – Another weak tropical wave is forecast to move across T&T on Tuesday, though activity associated with this wave will be more isolated to scattered than the previous two waves. Favorable upper-level conditions may allow for severe thunderstorms to develop across Western and hilly areas of Trinidad by the late morning through the afternoon, aided by the ITCZ as it drifts southwards.

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&TThere are no direct tropical threats facing T&T over the next 5 days. The passages of Tropical Waves 19 through 21 and the ITCZ are forecast to bring isolated to widespread showers and isolated to scattered thunderstorms beginning during the second half of Sunday through Tuesday, with peak inclement weather forecast on Monday. The main hazards include heavy rainfall, reducing visibility, and gusty winds up to and in excess of 55 KM/H. Street flooding is likely, with flash flooding possible. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage.

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 Depression Five

Tropical Depression Five details as of 5:00 PM AST Saturday 4th July 2020. Click for more information.
Tropical Depression Five details as of 5:00 PM AST Saturday 4th July 2020. Click for more information.

Tropical Depression Five has formed in the Western Atlantic, forecast to bring heavy rainfall and gusty winds to Bermuda.

If this system is named Edouard, it would be the earliest on record the Atlantic Basin records its 5th named storm. This system poses no threat to T&T and the Eastern Caribbean.

Tropical Wave 19 & The ITCZ

Tropical Wave 19 is analyzed along 56W, with much of the activity located where the wave interacts with the ITCZ, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms (Weathernerds)
Tropical Wave 19 is analyzed along 56W, with much of the activity located where the wave interacts with the ITCZ, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms (Weathernerds)

As of the 5:00 PM Tropical Update, the 19th tropical wave for the 2020 Atlantic Hurricane Season is located along 56W, from 18N southward based on our analysis. The wave axis is moving westward around 10 knots (18 KM/H).

Much of the activity associated with this wave is embedded within the ITCZ, with a large moisture plume surrounding the wave axis.

Models continue to show that this wave, its associated moisture, and the ITCZ will move across Trinidad and Tobago during the latter half of Sunday, bringing inclement weather. See below for details.

Tropical Wave 20 & The ITCZ

Tropical Wave 20 is analyzed along 49W, with little convective activity associated with the wave axis (Weathernerds)
Tropical Wave 20 is analyzed along 49W, with little convective activity associated with the wave axis (Weathernerds)

As of the 5:00 PM Tropical Update, further east, the axis of Tropical Wave 20 is approximately along 49W from 22N southward, moving west at 10 knots (18 KM/H).

This wave is forecast to move across T&T on Monday, keeping the ITCZ across the area and bringing widespread showers and isolated to scattered thunderstorm activity. See below for details.

Tropical Wave 21 & The ITCZ

Tropical Wave 21 is analyzed along 35W, with little convective activity associated with the wave axis (Weathernerds)
Tropical Wave 21 is analyzed along 30W to 35W, with little convective activity associated with the wave axis (Weathernerds)

As of the 5:00 PM Tropical Update, further east, the axis of Tropical Wave 21 is approximately at 30W to 35W from 22N southward, moving west at 15-20 knots (28-38 KM/H). This tropical wave is embedded within the ITCZ.

This wave is forecast to move across the region on Tuesday, with much of the modeled activity remaining north of T&T. However, favorable upper-level conditions may allow for strong thunderstorm activity across Trinidad. See below for details.

What does all of this mean for Trinidad and Tobago?

The Remainder of Saturday: Mostly settled conditions are forecast through the night, with partly cloudy skies. One or two brisk isolated showers are possible.

Seas to remain moderate, with waves near 2.0 meters in open waters, occasionally up to 2.5 meters. In sheltered areas, near 1.0 meter.

No adverse weather impacts forecast, though air quality will be at moderate, improving by nightfall into Sunday.


Sunday: During the early morning, mostly hot, sunny and somewhat hazy conditions, mainly across the northern half of Trinidad and Tobago. By the mid-morning through the afternoon, moisture associated with Tropical Wave 19 and the ITCZ will move across T&T. After midday, isolated to scattered showers and isolated thunderstorms are forecast to affect Eastern and Southern Trinidad, gradually spreading across the islands through the evening. These conditions are forecast to settle by the late evening, with isolated showers possible. A resurgence of activity is forecast after nightfall, ahead of Tropical Wave 20.

Seas to remain moderate, with waves up to 2.0 meters in open waters. In sheltered areas, less than 1.0 meter. Note that in heavier showers or thunderstorms, seas may become locally choppy or rough. Air quality to improve by mid-Sunday.

The main hazards, mainly during the second half of Sunday, would be locally heavy rainfall, reducing visibility, and localized wind damage from wind gusts associated with heavier showers or thunderstorms. 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.



Monday: An active ITCZ interacting with Tropical Wave 20 is forecast to be present across Trinidad and Tobago, with scattered to widespread showers and isolated to scattered thunderstorms forecast across both islands. Severe weather is likely. Activity is forecast to begin after midnight, peaking during the morning, gradually settling by the late afternoon across both islands with isolated showers across both islands into the night.

Seas to remain moderate, with waves up to 2.0 meters in open waters. In sheltered areas, less than 1.0 meter. Note that in heavier showers or thunderstorms, seas may become locally choppy or rough. Air quality to be at good levels.

The main hazards would be locally heavy rainfall, reducing visibility, and localized wind damage from wind gusts associated with heavier showers or thunderstorms. 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.


Tuesday: The axis of Tropical Wave 21 is forecast to move across T&T, with much of the activity remaining north of the islands. Across Trinidad and Tobago, isolated showers are forecast to interrupt a mostly settled morning, isolated strong thunderstorms are possible by the late morning through the afternoon, favoring Western areas of Trinidad. This will likely be triggered due to a combination of localized climatic effects, TW21 and the ITCZ. Conditions are forecast to settle by the evening into the night, with brisk, isolated showers possible.

The main hazards would be locally heavy rainfall, reducing visibility, and localized wind damage from wind gusts associated with heavier showers or thunderstorms. 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. On Tuesday, given light winds are forecast across Western Trinidad, and severe thunderstorms are possible, localized severe street/flash flooding and funnel cloud activity are possible.

Seas to remain moderate, with waves up to 2.0 meters in open waters. In sheltered areas, less than 1.0 meter. Note that in heavier showers or thunderstorms, seas may become locally choppy or rough. Air quality to be at good levels.



Wednesday: As the ITCZ drifts southward, isolated to scattered showers are forecast after midnight through the early morning, with heavier activity remaining offshore and favoring Eastern Trinidad and Tobago. A few of these showers are forecast to move across both islands during the late morning through the afternoon. A surge of Saharan Dust is forecast to move across T&T by the evening, with air quality returning to moderate.

The main hazards continue to be gusty winds and localized street flooding in isolated heavy showers. There is a low to medium chance of a thunderstorm.

Seas to remain moderate, with waves increasing up to 2 meters in open waters, occasionally above 2.0 meters by nightfall. In sheltered areas, near 1.0 meter.


Thursday into Friday: As Saharan Dust briefly blankets the region, mostly hazy skies are forecast with settled conditions. Brisk, isolated showers are possible throughout the day, remaining settled by the evening. However, by nightfall, models show another Tropical Wave-ITCZ event is forecast into Friday, with scattered to widespread showers and isolated thunderstorms moving across the islands into the weekend.

Possible Impacts This Week

Winds: Sustained surface winds between 35 KM/H and 50 KM/H are forecast by the later end of the week, with gusts up to and in excess of 55 KM/H possible in heavy showers or thunderstorms across Trinidad and Tobago, particularly on Sunday through Tuesday.

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

Sunday: Generally between 5-15 millimeters, favoring the afternoon through evening hours, with isolated totals up to 50 millimeters in heavy showers, thunderstorms and across Central and Southern Trinidad.

Monday: Widespread totals between 10-30 millimeters with isolated totals in heavier showers and thunderstorms up to 50 millimeters. Monday is forecast to be the wettest day during the forecast period.

Tuesday: Generally between 5-15 millimeters, with isolated totals up to 30 millimeters in heavy showers, thunderstorms and across Western areas.

Wednesday: Less than 10 millimeters across both islands with little rainfall accumulations forecast.

Thursday: Less than 10 millimeters across both islands with little rainfall accumulations forecast. Isolated totals up to 15 millimeters possible

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.

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.

Isolated to scattered activity is forecast Sunday through Tuesday, with widespread activity forecast on Monday. Highly isolated activity forecast on Wednesday and Thursday.

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

Tropical Cyclone Climatology

Tropical Cyclone Points of Origin during the first week of July July. Though much of the points of origin are west or north of T&T as we move through the second month of the Hurricane Season, we 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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