Tropical Update: Three Tropical Waves But No Significant Rainfall

Tropical Update Overview:
There are no systems in the Atlantic, as of 2 PM Tuesday, being officially monitored for tropical cyclone development.
Tropical Wave 23 – A large tropical wave in the Central Atlantic is forecast to move across T&T between Thursday and Friday, dragging the ITCZ slightly north. However, no significant rainfall is forecast.
Tropical Wave 24 – Another large, tropical wave is in the East Atlantic, with a large moisture plume, is moving across the Atlantic Ocean. This wave is forecast to move across the region this weekend into next week, with any activity remaining north of T&T
Tropical Wave 25 – A tropical wave is just moving off the Western African Coast, forecast to move across the region by mid-next week. It is too soon to tell what impacts this wave may have, if any, on the region. However, there is little support for tropical cyclone formation as of the 12Z model runs on Tuesday afternoon.

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. Tropical-wave-enhanced rainfall is forecast to be limited, with possible ITCZ activity on Thursday. However, beginning on Wednesday, a typical wet season pattern is forecast with isolated afternoon activity. The main hazards include highly isolated heavy rainfall, favoring Western Trinidad during 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. Funnel cloud activity is possible on Wednesday, mainly on Thursday.

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 23

Tropical Wave 23 is analyzed from 27N and 45W to 47W, with little convective activity as of today's Tropical Update due to dry mid-level conditions as a result of Saharan Dust. (Weathernerds)
Tropical Wave 23 is analyzed from 27N, along 45W to 47W, with little convective activity as of today’s Tropical Update due to dry mid-level conditions as a result of Saharan Dust. (Weathernerds)

As of the 4:00 PM Tropical Update, the 23rd tropical wave for the 2020 Atlantic Hurricane Season is located from 27N, along 45W to 47W 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, limiting convection, with nearly all of its activity near the southern area of the wave axis, where the axis interacts with the ITCZ.

Models continue to show that this wave may drag the ITCZ northward on Thursday into Friday across Trinidad and Tobago, though widespread shower activity is not forecast at this time. See below for details.

Tropical Wave 24

Tropical Wave 24 is analyzed further east from 25N southward along 32W, with isolated showers within 120 nautical miles of the wave axis where the wave interacts with the ITCZ. (Weathernerds)
Tropical Wave 24 is analyzed further east from 25N southward along 32W, with isolated showers within 120 nautical miles of the wave axis where the wave interacts with the ITCZ. (Weathernerds)

As of the 4:00 PM Tropical Update, the 24th tropical wave for the 2020 Atlantic Hurricane Season is located from 25N southward along 32W, 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 quell Saharan Dust concentrations across the Atlantic over the next week or so.

Models show that this wave and much of its associated moisture will remain north of Trinidad and Tobago this weekend, with a minor surge of moisture across T&T this weekend. See below for details.

Tropical Wave 25

Tropical Wave 25 is analyzed from 20N southward, from 18W to 15W, with much of the activity confined to the ITCZ. (Weathernerds)
Tropical Wave 25 is analyzed from 20N southward, from 18W to 15W, with much of the activity confined to the ITCZ. (Weathernerds)

As of the 4:00 PM Tropical Update, the 25th tropical wave for the 2020 Atlantic Hurricane Season analyzed from 20N southward, from 18W to 15W. 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.

What does all of this mean for Trinidad and Tobago?

Remainder of Tuesday: Mostly settled, barring the odd isolated shower after midnight. Saharan Dust concentrations remain high, with air quality between Moderate to Unhealthy for Sensitive Groups.

Seas forecast to be slight, with waves between 1.0 and 1.5 meters in open waters. In sheltered areas, near calm.

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


Wednesday – An upper-level trough will induce a mid to low-level trough across the region. This deep-layered trough system is forecast to significantly weaken winds across the region and enhance low-level convergence and moisture.

AM: Barring the odd brisk, isolated shower, a mostly sunny start is forecast. By the mid to late morning, partly cloudy skies are forecast to develop across coastal areas of both islands.

PM: By midday, isolated showers are forecast to favor Southern, hilly an and Western coastal areas. Isolated thunderstorms are forecast to favor Western Coastal Trinidad. These showers are forecast to interrupt partly cloudy skies and overall hot conditions, settling by the evening into the night.

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. Note that with weak winds, with sea breeze convergence, heat, and orographic effects acting as triggers for shower and thunderstorm development, funnel cloud activity is possible.

Seas forecast to be slight, with waves between 1.0 and 1.5 meters in open waters. In sheltered areas, near calm.



Thursday – An upper-level trough will induce a mid to low-level trough across the region. This deep-layered trough system is forecast to significantly weaken winds across the region and enhance low-level convergence and moisture. Tropical Wave 23 is forecast to move across the region, possibly dragging the ITCZ across Trinidad.

AM: Barring the odd brisk, isolated shower, a mostly sunny start is forecast. By the mid to late morning, partly cloudy skies are forecast to develop across coastal areas of both islands.

PM: By midday, isolated to scattered showers are forecast to favor Southern, hilly an and Western coastal areas. Isolated thunderstorms are forecast to favor Western Coastal Trinidad. These showers are forecast to interrupt partly cloudy skies and overall hot conditions, settling by the evening. Isolated showers, favoring Southern and Eastern Trinidad are possible through the night, gradually moving west.

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. Note that with weak winds, with sea breeze convergence, heat, and orographic effects acting as triggers for shower and thunderstorm development, funnel cloud activity is possible.

Seas forecast to be slight, with waves between 1.0 and 1.5 meters in open waters. In sheltered areas, near calm.



Friday – The axis of Tropical Wave 23 will move west of T&T, with the ITCZ slowly drifting south across T&T. Weak winds will persist across the region. Hence, localized heavy afternoon showers and thunderstorms are possible.

AM: Isolated to scattered showers are forecast, mainly favoring offshore areas and north of T&T after midnight but by sunrise, moving across Tobago. Isolated showers will favor Tobago and Northern Trinidad though the morning with mostly sunny skies elsewhere.

PM: By midday, isolated to scattered showers are forecast to favor Southern, hilly an and Western coastal areas. Isolated thunderstorms are forecast to favor Western Coastal Trinidad. These showers are forecast to interrupt partly cloudy skies and overall hot conditions, settling by the evening, with few brisk isolated showers through the night.

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.

Seas forecast to be slight, with waves between 1.0 and 1.5 meters in open waters. In sheltered areas, near calm.


Saturday, through the weekend – Similar to the past three days, after a mostly sunny early to mid-morning, partly cloudy skies are forecast to build. By midday through the afternoon, isolated afternoon showers and thunderstorms are possible, favoring Western, Southern, and hilly areas of Trinidad mainly. These conditions will interrupt mostly sunny and hot conditions.

Seas are forecast to be slight, with waves near or below 1 meter in open waters and near calm in sheltered areas.

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.

High Temperatures

As winds become unusually calm across the region beginning on Wednesday, temperatures are forecast to soar during the late morning through the afternoon.

Maximum high temperatures are forecast between 32°C and 35°C across Trinidad, with higher temperatures in urbanized areas while across Tobago, between 31°C and 33°C.

Overnight lows are forecast between 24°C and 26°C across Trinidad, with higher temperatures in urbanized areas while across Tobago, between 25°C and 27°C.

The heat index, or what outside feels like, may reach in the upper thirties to mid-forties.

The Heat Index

The heat index and is a combination of air temperature and relative humidity determining what the air feels like to a person i.e. how hot it actually feels.

The heat index is important because of sweating. Your body sweats in order to cool the skin and maintain a constant, healthy body temperature. This cooling process means that the sweat has to evaporate off the skin to remove heat. However, if the sweat is unable to evaporate, the body isn’t able to regulate temperature.

With high volumes of moisture in the air, also known as high relative humidity, which T&T regularly experience due to its tropical climate, the rate of sweat evaporation decreased. This is because the atmosphere is unable, or has limited potential to hold additional moisture in the atmosphere.

This results in you feeling warmer in humid conditions and cooler in less humid conditions i.e. when relative humidity decreases. As temperature increases, the heat index increases. As relative humidity increases, so does the heat index.

 Heat Index Values Explained
Heat Index Values Explained

Heat index is generally classified into four categories: caution, extreme caution, dangerous and extremely dangerous. Generally across Trinidad and Tobago, we experience heat indices of caution to extreme caution in times of hot days, with isolated areas experiencing dangerous heat indices such as urban areas.

Heat Safety

Graphic: Beat the Heat. Heat related deaths are preventable.

Graphic: Beat the Heat. Heat related deaths are preventable.

Source: MEMA
Heat Safety Tips and Resources
Heat Safety Graphic. Source: Heat Safety Tips and Resources

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

Daily, no rainfall to trace accumulations are forecast across Trinidad and Tobago. In areas where slow-moving isolated showers occur, up to 15 millimeters are possible daily, mainly on Thursday through Saturday. In highly isolated areas with thunderstorms, highly isolated totals in excess of 25 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 through the week, as no organized tropical systems are forecast to affect T&T as of this tropical update.

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

Tropical Cyclone Climatology

Tropical Cyclone Points of Origin during the second and third weeks of July.

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