Tropical Update: Tropical Waves To Bring Showers, Isolated Thunderstorms

Tropical Update Overview:
Post-Tropical Storm Dolly – Tropical Storm Dolly weakened into a post-tropical remnant low on Wednesday morning. No further advisories will be issued.
Tropical Wave 13 – A weak, southerly tropical wave moved across Trinidad on Wednesday, with much of the activity remaining across Venezuela and Guyana. This wave will trigger additional showers Wednesday night into early Thursday across the southern areas of Trinidad.
Tropical Wave 14 – A fast-moving tropical wave is forecast to move across Trinidad and Tobago late Thursday, ahead of another significant surge of Saharan Dust. A low-level jet may enhance winds, producing gusty winds up to and in excess of 60 KM/H.
Tropical Wave 15 – Another fast-moving tropical wave in the East Atlantic, embedded within the ITCZ is forecast to move across the region mid-next week, possibly dragging the ITCZ across T&T on Friday. A low-level jet may enhance winds, producing gusty winds up to and in excess of 60 KM/H.

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 passage of Tropical Wave 14 is forecast to bring isolated to scattered showers and isolated thunderstorms Thursday into early Friday. While locally heavy rainfall is possible, though a widespread inclement weather event is not expected, gusty winds up to and in excess of 60 KM/H will be the main hazard. Street flooding is possible, with flash flooding lesser so. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, localized wind damage and locally rough seas.

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 13

Tropical Wave 13 is analyzed along 63W, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms south and west of Trinidad and Tobago. (Weathernerds)
Tropical Wave 13 is analyzed along 63W, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms south and west of Trinidad and Tobago. (Weathernerds)

As of the 10:30 PM Tropical Update, the 13th tropical wave for the 2020 Atlantic Hurricane Season is located along 63W, from 10.5N southward based on our analysis. The wave axis is moving westward around 15-20 knots (28-37 KM/H).

Much of the activity associated with this wave remained south of Trinidad and Tobago, triggering a few showers and gusty winds across Trinidad today.

This wave is forecast to progress westward, bringing showers and thunderstorms to parts of Venezuela through the next day or so, with only a few showers possible associated with this wave overnight across Southern Trinidad.

Tropical Wave 14

Tropical Waves 13 (at 63W) and 14 (at 50-55W) in the Atlantic Ocean (Weathernerds)
Tropical Waves 13 (at 63W) and 14 (at 50-55W) in the Atlantic Ocean (Weathernerds)

As of the 10:30 PM Tropical Update, further east, the axis of Tropical Wave 14 is approximately along 50W to 55W from 21N southward, moving west at 15-20 knots (28-37 KM/H).

Model guidance continues to show this wave moving across the region by late Thursday with moisture beginning to affect both islands after midnight into the day.

Presently, this wave has favorable upper level divergence, marginally favorable low-level convergence and an abundant moisture envelope. This moisture is chiefly responsible for our improving air quality. However, a dense surge of Saharan Dust is forecast to follow the passage of the wave into Friday.

Wind shear is forecast to remain favorable to marginal allowing for convection to develop but an already dry atmosphere and negligible upper atmosphere support may make conditions unfavorable for deep, persisting thunderstorms and heavy showers.

A low-level jet, a narrow band of fast moving winds at low-levels of the atmosphere, is forecast to accompany this tropical wave, with a surge of winds following into the weekend. This feature is forecast not only to agitate seas but bring gusty winds up to and in excess of 60 KM/H beginning Thursday through Sunday.

In showers and thunderstorms, stronger winds may mix down to the surface, producing downbursts and areas of wind damage, particularly across Northern Trinidad and Tobago.

Tropical Wave 15

Tropical Waves 13 (at 63W), 14 (at 50-55W), and 15 (30W to 35W) in the Eastern Atlantic Ocean, embedded within the ITCZ. (Weathernerds)
Tropical Waves 13 (at 63W), 14 (at 50-55W), and 15 (30W to 35W) in the Eastern Atlantic Ocean, embedded within the ITCZ. (Weathernerds)

As of the 10:30 PM Tropical Update, further east, the axis of Tropical Wave 15 is approximately at 30W to 35W from 15N southward, moving west at 20 knots (37 KM/H). This tropical wave is embedded within the ITCZ.

This tropical wave is forecast to move across the entire Lesser Antilles on Saturday, with moisture and possibly the ITCZ affecting the region from late Friday through Saturday. At this time, though the ITCZ will be present, widespread significant and heavy rainfall is not anticipated.

A low-level jet, a narrow band of fast moving winds at low-levels of the atmosphere, is forecast to accompany this tropical wave, with a surge of winds following into the weekend. This feature is forecast not only to agitate seas but bring gusty winds up to and in excess of 60 KM/H beginning Thursday through Sunday.

In showers and thunderstorms, stronger winds may mix down to the surface, producing downbursts and areas of wind damage, particularly across Northern Trinidad and Tobago.

See below for details.

What does all of this mean for Trinidad and Tobago?

Thursday: After an initially settled morning, isolated to scattered showers are forecast to develop across Trinidad, with heavier showers favoring Southern and Eastern areas. By midday through the afternoon, isolated thunderstorms and showers are forecast to affect both islands, with heavier activity remaining offshore and north of T&T. Activity is forecast to persist into the night, gradually settling.

Gusty winds, up to and in excess of 60 KM/H and street 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. Localized power dips/outages, downed trees and wind damage possible.


Friday: As the axis of Tropical Wave 14 moves west, following some early morning showers, a severe surge of Saharan Dust will move in across the islands, with higher concentrations across Tobago and north of the country. Winds are also forecast to pick up across the region, with strong gusts possible throughout the day, particularly ahead of and during showery activity. The main hazard would be reduced air quality, visibility, and localized wind damage from wind gusts, particularly overnight as moisture ahead of Tropical Wave 15 nears the islands, with the ITCZ.

Gusty winds, up to and in excess of 60 KM/H possible. Seas to remain moderate to rough, with waves up to 2.5 meters in open waters, occasionally up to 3.0 meters. In sheltered areas, near 1.0 meter but choppy due to a brief long period swell event late Friday through early Sunday. Air quality forecast to lower to unhealthy levels by nightfall.



Saturday: The axis of Tropical Wave 15 will be nearing the Lesser Antilles, dragging the ITCZ and associated moisture near to the islands, increasing cloudiness and isolated showers are forecast, with heavier activity favoring Trinidad. Conditions are forecast to settle by the late afternoon, with isolated showers possible as the ITCZ drifts south, while the wave axis nears.

Gusty winds, up to and in excess of 60 KM/H likely, with wind gusts up to 80 KM/H possible. Seas to remain moderate to rough, with waves up to 3.0 meters. In sheltered areas, near 1.0 meter but choppy due to a brief long period swell event through early Sunday. Air quality forecast to initially improve, and gradually reduce by late-night as a high-pressure system regains dominance.


Sunday: A high-pressure system, with dense Saharan Dust and breezy conditions, continues to dominate across Trinidad and Tobago. A mostly dull and hazy day is forecast. Regardless, the main hazards continue to be reduced air quality, visibility. Overall winds are forecast to decrease.

Gusty winds, up to 55 KM/H possible. Seas to remain moderate to rough, with waves up to 3.0 meters initially, then up to 2.5 meters by nightfall. In sheltered areas, near 1.0 meter. Air quality forecast to remain at unhealthy levels to unhealthy for sensitive groups.


Monday: high-pressure system, with dense Saharan Dust and breezy conditions, continues to dominate across Trinidad and Tobago. A mostly dull and hazy day is forecast. Regardless, the main hazards continue to be reduced air quality, visibility. Overall winds are forecast to decrease.

Seas to remain at moderate levels, 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.


Possible Impacts This Week

T&T’s Risk Matrix for Tropical Wave 14

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.

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

Thursday: Daily rainfall accumulations are forecast to be between 10-20 millimeters, with isolated totals up to 35 millimeters, favoring Eastern and Southern halves of Trinidad, with similar possible totals across isolated Western Trinidad.

Friday: Little overall rainfall accumulations forecast, with isolated totals up to 5 millimeters in areas that experience isolated heavy showers.

Saturday: Less than 5-10 millimeters across both islands, with isolated totals up to 45 millimeters, particularly across Trinidad in areas that experience heavy downpours and localized thunderstorms, favoring Eastern Trinidad.

Sunday: Little overall rainfall accumulations forecast, with isolated totals up to 5 millimeters in areas that experience isolated heavy showers.

Monday: Less than 5-10 millimeters across both islands, with isolated totals up to 20 millimeters, particularly across Trinidad in areas that experience heavy downpours and localized thunderstorms, favoring Eastern 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.

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 through the next 5 days, with scattered activity likely during the second half of Thursday, and Friday night into Saturday.

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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