Tropical Update: Tropical Waves, ITCZ To Bring Rainfall, Inclement Weather To T&T

Tropical Update Overview:
There are no systems east of Trinidad and Tobago, as of 2 PM Wednesday, being officially monitored for tropical cyclone development.
Tropical Wave 31 – A large tropical wave in the Central Atlantic is forecast to move across T&T between Thursday and Friday, dragging the ITCZ towards our area. Isolated, heavy rainfall, and inclement weather likely on Thursday into Friday.
Tropical Wave 32 – Another tropical wave is in the Central Atlantic, with a large moisture plume, is moving across the Atlantic Ocean. This wave is forecast to move across the region this weekend, keeping the ITCZ across T&T. Models disagree on overall rainfall outputs. Locally heavy rainfall is possible.
Tropical Wave 33 – A tropical wave in the East Atlantic, forecast to move across the region Monday into Tuesday, with models agreeing on a heavy rainfall event as the ITCZ will remain across T&T.

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&TThere are no direct tropical threats facing T&T over the next 5 days, at this time. Tropical-wave-enhanced rainfall, interacting with the ITCZ is anticipated on Thursday into Friday, Saturday, and Monday into Tuesday. Models disagree on inclement weather from Sunday through Tuesday. The main hazards include isolated to scattered areas of heavy rainfall, favoring Trinidad during two time periods: after midnight through the early morning and again during the late morning through the afternoons, reducing visibility, and gusty winds up to and in excess of 55 KM/H. Street or flash flooding will be possible in slow-moving showers and thunderstorms. 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 Wave 31

Tropical Wave 31 is analyzed from 20N, along  53W to 55W, most of the convective activity north and east of T&T. Activity is forecast to spread across T&T on Thursday as this wave interacts with the ITCZ. (Weathernerds)
Tropical Wave 31 is analyzed from 20N, along 50W to 55W, most of the convective activity north and east of T&T. Activity is forecast to spread across T&T on Thursday as this wave interacts with the ITCZ. (Weathernerds)

As of the 6:00 PM Tropical Update, the 31st tropical wave for the 2020 Atlantic Hurricane Season is located from 20N, along 50W to 55W based on our analysis. The wave axis is moving westward around 10 to 15 knots (18 to 27 KM/H).

Much of this wave is surrounded by Saharan Dust to its west, north, and east. Convective activity is firing along the northern portion of the wave, but activity is forecast to spread across T&T on Thursday and Friday as this wave interacts with the ITCZ. Scattered to widespread showers and isolated to scattered thunderstorms are in the forecast. See below for details.

Tropical Wave 32

Tropical Wave 32 is analyzed further east from 20N southward along 41/42W, with isolated to scattered showers within 120 nautical miles of the wave axis where the wave interacts with the ITCZ. (Weathernerds)
Tropical Wave 32 is analyzed further east from 20N southward along 42/44W, with isolated to scattered showers within 120 nautical miles of the wave axis where the wave interacts with the ITCZ. (Weathernerds)

As of the 6:00 PM Tropical Update, the 32nd tropical wave for the 2020 Atlantic Hurricane Season is located from 20N southward along 42/44W, based on our analysis. The wave axis is moving westward around 10 to 15 knots (18 to 27 KM/H).

This wave has a large area of moisture, as seen on precipitable water imagery. This wave is forecast to keep Saharan Dust concentrations across the Atlantic north of Trinidad and Tobago.

Models show that this wave and much of its associated moisture will affect T&T this weekend, though there are some disagreements on timing. See below for details.

Tropical Wave 33

Tropical Wave 33 is analyzed from 15N southward, at 30W, with much of the activity confined to the ITCZ. (Weathernerds)
Tropical Wave 33 is analyzed from 15N southward, at 30W, with much of the activity confined to the ITCZ. (Weathernerds)

As of the 6:00 PM Tropical Update, the 33rd tropical wave for the 2020 Atlantic Hurricane Season analyzed from 15N southward, along 30W. The wave axis is moving westward around 10 to 15 knots (18 to 27 KM/H).

Much of the activity associated with this wave is confined to the ITCZ. This wave is forecast to move into a marginally supportive environment this week, with models showing some indication of organization as the wave moves into the Central Atlantic.

However, no models bring an organized tropical cyclone into the Lesser Antilles mid-next week, keeping this wave as a strong tropical wave.

It is still too soon to forecast exactly what impacts, if any this wave may bring to the islands but it does bring the threat of inclement weather on Election Day (Monday 10th August 2020) into Tuesday, but models continue to disagree on just how much precipitation that this wave and the ITCZ may generate. See below for details.

What does all of this mean for Trinidad and Tobago?

Remainder of Wednesday: Mostly settled, barring the odd isolated shower nearing midnight, favoring Eastern areas of both islands, gradually moving westward.

Seas forecast to be moderate, with waves between 1.5 and 2.0 meters in open waters. In sheltered areas, below 1.0 meter, but becoming choppy in showers and thunderstorms.

No adverse weather impacts forecast.


Thursday – Upper-level conditions will support inclement weather as Tropical Wave 31 moves across T&T, with activity enhanced by the ITCZ and weak wind shear. Winds are forecast to be light, from the south to southeast.

AM: After midnight, isolated showers and thunderstorms are possible, favoring offshore areas and gradually moving westward. A brief lull in activity is expected by daybreak, with mostly sunny skies across both islands, but showers and thunderstorms are forecast again by the late morning, interrupting variably cloudy skies.

PM: By the late morning through the afternoon, scattered to widespread showers and thunderstorms are forecast to interrupt mostly cloudy to overcast skies across both islands. This activity is forecast to settle by the evening into the night., with isolated showers possible. A resurgence of activity after midnight is forecast.

The main hazards include isolated to scattered areas of heavy rainfall across both islands, reducing visibility, and gusty winds up to and in excess of 55 KM/H. Street or flash flooding will be possible in slow-moving showers and thunderstorms. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage. Note that with weak winds, with sea breeze convergence, heat, and orographic effects acting as triggers for shower and thunderstorm development.

Seas forecast to be moderate, with waves between 1.5 and 2.0 meters in open waters. In sheltered areas, below 1.0 meter, but becoming choppy in showers and thunderstorms.



Friday – Tropical Wave 31 will be moving westward, Tropical Wave 32 will be nearing T&T and the ITCZ will remain across both islands. A favorable convergent/confluent environment will support showers and thunderstorms. Winds forecast to be light, from the southeast to east.

AM: Early morning showers and thunderstorms are forecast after midnight, continuing through the day, interrupting sunny skies. By the late morning, isolated showers or thunderstorms may develop interrupting cloudy periods across both islands.

PM: This late morning through the afternoon showers and thunderstorms will favor Trinidad, still interrupting cloudy skies. Activity will settle by the evening, with a few isolated showers into the night. Given that the ITCZ will remain across T&T, a resurgence in activity is forecast after midnight.

The main hazards include isolated to scattered areas of heavy rainfall across both islands, reducing visibility, and gusty winds up to and in excess of 55 KM/H. Street or flash flooding will be possible in slow-moving showers and thunderstorms. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage. Note that with weak winds, with sea breeze convergence, heat, and orographic effects acting as triggers for shower and thunderstorm development.

Seas forecast to be moderate, with waves between 1.5 and 2.0 meters in open waters. In sheltered areas, below 1.0 meter, but becoming choppy in showers and thunderstorms.



Saturday – The axis of Tropical Wave 32 will move across T&T, with the ITCZ remaining across the islands. Weak winds will persist across the region.

AM: After midnight, heavy showers and isolated thunderstorms are forecast to favor eastern areas, gradually moving across Trinidad initially, then Tobago, continuing through midday, gradually becoming settled as the day progresses.


This is where models significantly diverge. The first group of top models shows Saharan Dust quelling shower and thunderstorm activity Saturday through Sunday. Top dust models show a surge of dust arriving on Saturday through Sunday, supporting this solution.

The second group of top models shows Saharan Dust remaining north of T&T, keeping heavy rainfall on tap for T&T through the weekend and into next week.

For now, we’ll err on the side of caution, going on the conservative side with settled weather late Saturday through early next week, but this can change as we near closer in the forecast period.


PM: After midday, conditions are forecast to settle with isolated showers possible through the evening, generally interrupting partly cloudy skies.

The main hazards include isolated to scattered areas of heavy rainfall across both islands, reducing visibility, and gusty winds up to and in excess of 55 KM/H. Street or flash flooding will be possible in slow-moving showers and thunderstorms. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage. Note that with weak winds, with sea breeze convergence, heat, and orographic effects acting as triggers for shower and thunderstorm development.

Seas forecast to be moderate, with waves between 1.5 and 2.0 meters in open waters. In sheltered areas, below 1.0 meter, but becoming choppy in showers and thunderstorms. Air quality is forecast to decrease to moderate levels at times.



Sunday – The forecast confidence is low to medium. A surge of Saharan Dust is forecast to continue moving across T&T, though concentrations will be mild. Isolated showers are possible after a mostly sunny early to mid-morning, By midday through the afternoon, isolated afternoon showers and thunderstorms are possible, favoring Western, Northern, and hilly areas of Trinidad mainly. These conditions will interrupt mostly sunny and hot conditions.

Seas forecast to be moderate, with waves between 1.5 and 2.0 meters in open waters. In sheltered areas, below 1.0 meter, but becoming choppy in showers and thunderstorms. Air quality is forecast to decrease to moderate levels at times.

The main hazards include highly isolated heavy rainfall, favoring the Western half of Trinidad, reducing visibility, and gusty winds up to and in excess of 55 KM/H. Street or flash flooding will be possible in slow-moving showers and thunderstorms. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage.


Monday into Tuesday – The forecast confidence is low to medium. Tropical Wave 33 will traverse T&T, reducing Saharan Dust concentrations. Isolated to scattered showers and isolated thunderstorms are possible by the late morning through the afternoon, mainly across Trinidad. Thunderstorm activity is forecast to favor Northern and Western Trinidad, interrupting mostly sunny and hot conditions. Conditions will settle by the evening with isolated overnight showers possible.

Seas forecast to be moderate, with waves between 1.5 and 2.0 meters in open waters. In sheltered areas, below 1.0 meter, but becoming choppy in showers and thunderstorms. Air quality is forecast to decrease to moderate levels at times.

The main hazards include highly isolated heavy rainfall, favoring the Western half of Trinidad, reducing visibility, and gusty winds up to and in excess of 55 KM/H. Street or flash flooding will be possible in slow-moving showers and thunderstorms. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage.

Possible Impacts Over Next 5-7 Days

There are no tropical systems that pose a direct threat to T&T over the next week, as of today’s tropical update. However, heavy rainfall is possible.

Winds

Sustained surface winds will be weak, generally below 25 KM/H during the afternoon at its peak. However, Gusts up to and in excess of 55 KM/H possible in heavy showers or thunderstorms across Trinidad and Tobago.

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

Thursday: Between 10-15 millimeters are forecast, with isolated totals between 20-35 millimeters possible. In slow-moving downpours or thunderstorms, up to 50 millimeters possible.

Friday: Between 10-15 millimeters are forecast, with isolated totals between 20-35 millimeters possible. In slow-moving downpours or thunderstorms, up to 50 millimeters possible.

Saturday: Between 10-15 millimeters are forecast, with isolated totals up to 20 millimeters possible. In slow-moving downpours or thunderstorms, up to 35 millimeters possible. These isolated higher totals are forecast to favor eastern and southern areas of Trinidad.

Sunday: Conservatively, little to no rainfall is forecast, with isolated totals up to 5 millimeters across both islands. However, if Saharan Dust remains north and ITCZ activity persists, Between 10-20 millimeters are possible, with isolated totals up to 35 millimeters possible. In slow-moving downpours or thunderstorms, up to 50 millimeters possible.

Monday: This rainfall forecast is highly uncertain. Conservatively, little to no rainfall is forecast, with isolated totals up to 10 millimeters across both islands. If ITCZ activity persists, between 20-35 millimeters are possible, with isolated totals up to 55 millimeters possible. In slow-moving downpours or thunderstorms, up to 75 millimeters possible.

Tuesday: This rainfall forecast is also highly uncertain. Conservatively, little rainfall is forecast, with isolated totals up to 10 millimeters across both islands. If ITCZ activity persists, up to 20 millimeters are possible, with isolated totals up to 35 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, with widespread showers and rain possible on Thursday through the first half of Saturday.

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

Tropical Cyclone Climatology

Tropical Cyclone Points of Origin during the first through third weeks of August.

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