Tropical Update: Tropical Wave 58 To Bring Showers, Thunderstorms to T&T on Monday

Tropical Update Overview:
Hurricane Pablo – Pablo became the 6th hurricane of the 2019 Atlantic Hurricane Season. This system is of no threat to land at this time.
Tropical Wave 57 – A weak tropical wave traversed the Lesser Antilles on Saturday 26th October. Minimal shower and thunderstorm activity are located near the wave axis, now in the Central Caribbean Sea.
Tropical Wave 58 – An active tropical wave is approaching Trinidad, Tobago and the Lesser Antilles. This wave is forecast to bring showers and thunderstorms on Monday and Tuesday, with localized severe weather possible. Acitivty from this tropical wave will be isolated to scattered, interrupting cloudy skies. Mositure from this wave will stick around through the week, increasing shower and thunderstorm chances.
Tropical Wave 59 – This tropical wave is forecast to move across Trinidad, Tobago and the Lesser Antilles by the end of this week, bringing another round of showers and thunderstorms. Elevated risk of street/flash flooding due to the forecast wet week ahead.
Impacts to T&T – Tropical Wave 58 will bring isolated to scattered showers and thunderstorms to T&T on Monday and Tuesday, with activity mainly occurring after 2:00 AM through the late afternoon on both days. Lingering moisture will fuel afternoon showers and thunderstorms across parts of both islands, mainly Northern and Western areas, on Wednesday and Thursday. Tropical Wave 59 will begin to affect T&T Friday into Saturday, with isolated to scattered showers again. No direct tropical threats to Trinidad and Tobago are forecast over the next week. We may experience street flooding and gusty winds in those heavier showers and thunderstorms.

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.

Hurricane Pablo

As of 11:00 AM Sunday AST, the National Hurricane Center continues to issue advisories on, now, Hurricane Pablo, 865 kilometers northeast of the Lajes Air Base in the Azores Islands.

Tropical Wave 57

Isolated showers associated with Tropical Wave 57 as it moves through the Central Caribbean Sea in this latest tropical update. Credit: Weathernerds
Isolated showers associated with Tropical Wave 57 as it moves through the Central Caribbean Sea in this latest tropical update. Credit: Weathernerds

The axis of Tropical Wave 57 is along 68W south of 20N, moving W around 15 kt. The wave continues to be very weak and difficult to track. The wave has scattered showers near the vicinity of the wave from 14N-17N between 65W-67W.

This wave moved through the Lesser Antilles with minimal impacts, beyond its effects on our overall wind regime in Trinidad and Tobago. No further impacts forecast to the Eastern Caribbean as it continues on its westward path.

Tropical Wave 58

Activity associated with Tropical Wave 58 along 52W nearing the Lesser Antilles with scattered showers and thunderstorms. Credit: Weathernerds
Activity associated with Tropical Wave 58 along 52W nearing the Lesser Antilles with scattered showers and thunderstorms. Credit: Weathernerds

As of the 4:00 PM Tropical Update, the axis of Tropical Wave 58 extends its axis along 52W from 15N southward, moving west at 10 to 15 knots. This wave is well-depicted in satellite imagery and latest ASCAT pass. Isolated to scattered moderate convection is from 09N-12N between 51W-56W.

No development of this wave is forecast, but welcome rainfall is expected mainly for Trinidad and Tobago, on Monday into Tuesday as this wave traverses the region.

Generally, less than 1 inch (25 millimeters) is expected, with up to 2 inches possible in isolated areas, mainly across Trinidad. No significant impacts are expected beyond isolated street/flash flooding and gusty winds in heavier showers and thunderstorms.

For Trinidad and Tobago, moisture from this wave will linger across the region throughout the week, fuelling heavier showers and thunderstorms resulting from daytime heating, sea breeze convergence, and orographic precipitation. See below for details.

Tropical Wave 59

Activity associated with Tropical Wave 58 along 52W nearing the Lesser Antilles with scattered showers and thunderstorms. Credit: Weathernerds

As of the 2:00 PM Tropical Weather Outlook and the 4:00 PM Tropical Update, Tropical Wave 59 is located extends its axis along 32W from 16N southward, moving W at 10-15 kt. Scattered moderate convection prevails from 02N-11N between 30W-36W. A 1012 millibar low is located just ahead of this wave near 05N34W to 04N36W, within the ITCZ.

No development is expected of this wave and its associated low-pressure as there is no model support.

The tropical wave is forecast to move across the Lesser Antilles later this week, between Friday and Saturday, bringing another round of showers and thunderstorms to Trinidad and Tobago.

Generally, less than 1 inch (25 millimeters) is expected, with up to 2 inches possible in isolated areas, mainly across Trinidad. No significant impacts are expected beyond isolated street/flash flooding and gusty winds in heavier showers and thunderstorms.

What does all of this mean for Trinidad and Tobago?

With the passage of Tropical Wave 58 on Monday into Tuesday, and Tropical Wave 59 Friday into Saturday, we are forecasting a relatively wet week ahead. But these showers and thunderstorms will be isolated to scattered during the passages of the tropical waves and mostly isolated Wednesday and Thursday, interrupting partly cloudy skies and favoring the afternoon hours. There are no tropical threats to T&T as of today’s tropical update.

On Monday, showers are forecast to begin interrupting partly cloudy skies mainly after 2:00 AM, continuing through the morning across both islands. By the late morning, near 11:00 AM, heavier showers and thunderstorms are forecast, mainly across Northern and Western Trinidad continuing through the afternoon, with isolated to scattered showers and periods of light rain. Conditions are forecast to become settled by the late afternoon into the evening, with a few isolated showers ongoing across eastern halves of both islands.

Similar conditions are forecast on Tuesday, with slightly more isolated showers and thunderstorms, and you may see a bit more sun! Monday is forecast to be the wetter of the two days.

On Wednesday and Thursday, an initially clear morning, at times with a few isolated showers during the pre-dawn through dawn will lead to a hot and sunny late morning. By midday, isolated showers and thunderstorms may develop across the western halves of mainly Trinidad, but also Tobago as well as hilly areas. Thunderstorms may favor western coastal Trinidad during the afternoon hours.

Moisture ahead of Tropical Wave 59 is forecast to begin moving across the islands on Thursday, but much of the activity of this wave is forecast to occur on Friday (the wetter of the two days) into Saturday. Similar to Monday, showers are forecast to begin interrupting partly cloudy skies mainly after 2:00 AM, continuing through the morning across both islands. By the late morning, near 11:00 AM, heavier showers and thunderstorms are forecast, mainly across Northern and Western Trinidad continuing through the afternoon, with isolated to scattered showers and periods of light rain. Conditions are forecast to become settled by the late afternoon into the evening, with a few isolated showers ongoing across eastern halves of both islands.

Activity will be isolated to scattered, with no widespread severe weather forecast. However, with all thunderstorms and heavy showers, there is the possibility of street flooding and gusty winds.

An unwanted by-product of this increased moisture will be particularly humid conditions across Trinidad and Tobago. This means that while the actual recorded temperature on some days may not top 33/34°C, that feels like temperature may easily top 40°C due to that high humidity, particularly on Wednesday and Thursday. However, those showers will bring some brief heat relief.

The Heat Index

The heat index 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

The 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.

This upcoming week, heat index levels are likely to remain at extreme cautious to dangerous levels. Heat cramps and heat exhaustion are likely with heatstroke probable with continued activity.

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

Impacts This Upcoming Week

Winds: Sustained surface winds between 15 KM/H and 30 KM/H with gusts in excess of 55 KM/H are possible in heavy showers or thunderstorms across Trinidad and Tobago throughout the week, particularly on Monday into Tuesday and Friday into Saturday.

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: Throughout the week, daily rainfall accumulations are forecast to be isolated totals of 5-10 millimeters, with up to 25 millimeters in isolated thunderstorms or heavy downpours.

On Monday into Tuesday and Friday into Saturday, 15-25 millimeters of rainfall is possible across mainly Trinidad, with isolated totals up to 50 millimeters in those highly localized thunderstorms and downpours.

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.

Hazardous Seas: A long period swell event is underway across Trinidad, Tobago, and the Eastern Caribbean. Coastal flooding may be exacerbated during heavy shower and thunderstorm activity.

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.

Throughout the week, mainly isolated activity is forecast, with the exception of Monday and Friday, where scattered activity is forecast.

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

Tropical Cyclone Climatology

Tropical Cyclone Points of Origin during the month of November. Though much of the points of origin are west or north of T&T as we move into the last 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.

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