Tropical Wave 11: No Direct Tropical Threat To T&T At This Time, Still Forecast To Bring Some Rainfall

What you need to know:
— Tropical Wave 11, a well-defined tropical wave, is being monitored by the National Hurricane Center for tropical cyclone formation. As of 8:00 AM Monday, it has low (20%) chances of development in 48 hours and 5 days respectively and the core of the system is expected to stay north of Trinidad and Tobago by the mid to end of the week. However, a band of moisture (not the Intertropical Convergence Zone) is forecast to begin affecting T&T by early Tuesday morning.
— Scattered showers and isolated thunderstorms are forecast to begin by Tuesday afternoon and continue through the end of the week, with periodic mostly cloudy to cloudy skies.
— There are no alerts, watches, or warnings in effect for T&T from the Trinidad and Tobago Meteorological Service at this time.

The Tropical Outlook

Tropical Weather Outlook as of 8:00 AM Monday 21st June 2021.
Tropical Weather Outlook as of 8:00 AM Monday 21st June 2021.

The National Hurricane Center (NHC) is monitoring a well-defined tropical wave (Tropical Wave 11), approximately 1,500 kilometers east of Trinidad and Tobago. The tropical wave is producing disorganized showers and thunderstorms. According to the NHC, some development of this disturbance will be possible during the next couple of days before upper-level winds become less conducive for further organization by Thursday.

The system is expected to move westward to west-northwestward at around 15 MPH (24 KM/H). As of 8:00 AM Monday 21st June 2021, the NHC has given this tropical disturbance a low (20%) chance of tropical cyclone formation over the next 48 hours and five days respectively.

Top global models show the tropical wave moving westward while the area of low pressure lags east of the Lesser Antilles, with the axis of the tropical wave moving across the islands on Tuesday into Wednesday, but the area of low pressure moving across the Windward Islands by the end of the week.

00Z June 21st 2021 EMCWF maximum wind gusts over the next 10 days showing a narrow area of 55 KM/H to 70 KM/H wind gusts associated with a tropical disturbance staying north of T&T and Barbados.
00Z June 21st 2021 EMCWF maximum wind gusts over the next 10 days showing a narrow area of 55 KM/H to 70 KM/H wind gusts associated with a tropical disturbance staying north of T&T and Barbados.

Over the last 12 hours, top global models have become less enthusiastic about development, even with additional convection developing along the wave axis. None of the operational runs of top global models show development, with only the EMCWF EPS ensembles having 65% reaching past tropical-depression-strength (20+ knots or 37 KM/H sustained winds) and less than 5% reaching tropical-storm-strength (34+ knots or 63 KM/H sustained winds). Notably, all ensemble model runs take the disturbance north of T&T, Grenada, and Barbados.

The Forecast

Total precipitable water imagery showing a band of moisture approaching T&T and the Windward Islands ahead of Tropical Wave 11 (the tropical disturbance being monitored for development)
Total precipitable water imagery showing a band of moisture approaching T&T and the Windward Islands ahead of Tropical Wave 11 (the tropical disturbance being monitored for development)

Monday: Generally hazy and slightly breezy conditions across T&T with a few isolated showers favoring Tobago initially and then across parts of Trinidad during the afternoon. Generally settled conditions are forecast through the evening, barring the odd shower. Increasing cloudiness with isolated showers across southern and eastern areas possible near and after midnight.

Tuesday: A mostly cloudy, becoming overcast, day is forecast across T&T, with brief sunny spells during the mid-morning across northwestern areas of Trinidad. By the afternoon, periods of rain, scattered showers, some of which becoming heavy, and scattered thunderstorms are forecast to interrupt cloudy skies.

Wednesday: A mostly cloudy to overcast day with periods of rain, scattered showers, some of which becoming heavy, and scattered thunderstorms. These conditions are forecast to briefly subside by the evening, with a resurgence in showers and isolated thunderstorms near and after midnight.

Thursday: A partly cloudy and hot day, with little to no wind, is forecast. Showers and isolated thunderstorms are forecast to develop by the late morning through the afternoon, favoring Trinidad. Heavier rainfall is forecast to favor western areas.

Friday: A mostly cloudy to overcast day with periods of rain, scattered showers, some of which becoming heavy, and scattered thunderstorms. Heavier rainfall to favor northern and western areas. These conditions are forecast to briefly subside by the evening, with a resurgence in showers and isolated thunderstorms near and after midnight.

Marine: Seas are forecast to be slight to moderate over the next 5 days, with waves between 1.0 to 2.0 meters in Trinidad and Tobago’s open waters. Across sheltered coastlines, waves below 1.0 meters are expected, with choppy seas in the vicinity and during heavy showers or thunderstorms. Note that King Tides will be ongoing from Tuesday. If Tropical Wave 11 develops, rough seas may be possible.

Forecast Discussion

There are two tropical waves of interest to T&T, forecast to be the main “weather-makers” this week but conditions will not be as simple as two tropical wave passages.

The first tropical wave, Tropical Wave 11, is producing a clustered area of showers and thunderstorms. This wave is forecast to continue to move westward over the next 24-48 hours. An area of low pressure is forecast to develop and detach from this wave, moving west-northwestward but at a much slower pace.

Tropical Wave 11 and Tropical Wave 12 are forecast to move across T&T and the Windward Islands on Wednesday into Thursday and Thursday into Friday with abundant moisture affecting the region from Tuesday into the weekend.

Compounding on the moisture and instability associated with the tropical waves is an upper-level trough enhancing activity from Wednesday into Thursday with favorable low-level convergence and upper-level divergence, supportive of heavy shower and thunderstorm development. Wind shear will be light to non-existent, allowing for heavy to violent rainfall to occur during shower or thunderstorm activity as well as localized climatic effects to allow heavy showers/thunderstorms to develop across T&T during the afternoon.

During the second half of the week, winds will be light to non-existent, with the prevailing wind direction from the south to southeast. With this wind profile and atmospheric conditions, there will be the possibility of funnel cloud development.

Infrared satellite imagery showing scattered showers east of Trinidad and Tobago associated with a band of moisture and the approaching Tropical Wave 11.
Infrared satellite imagery showing scattered showers east of Trinidad and Tobago associated with a band of moisture and the approaching Tropical Wave 11.

Temperatures

On days with mostly cloudy to overcast skies are forecast, maximum high temperatures are forecast to be near or below 31.0°C. On days with partly cloudy to mostly cloudy skies, particularly Thursday into Friday, maximum high temperatures may reach as high as 34.0°C. Overnight lows across both islands are forecast to be between 24.0°C and 26.0°C over the next 5 days.

Forecast Impacts

Forecast impacts due to Tropical Wave 07

Mainly from Tuesday afternoon through the end of the week, the main hazards include localized to scattered heavy rainfall triggering street flooding and flash flooding. Depending on where the rain falls, there is a very low chance of riverine flooding across Trinidad at this time. Lightning and gusty winds up to and in excess of 60 KM/H may accompany thunderstorms or heavy showers and cause power dips/outages, downed trees, and localized wind damage.

Winds

Sustained surface winds are forecast to be light to nonexistent during the latter half of the week. In shower and thunderstorm activity, gusts up to and in excess of 60 KM/H are possible. 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.

Rainfall

Over the next 5 days, rainfall accumulations between 25-50 millimeters are forecast, with higher totals up to 75 millimeters in localized areas. However, highly localized totals up to and in excess of 100 millimeters are possible in prolonged heavy showers or isolated thunderstorm activity over the next 5 days. Note that highly isolated areas across western and northern areas of Trinidad may exceed daily forecast totals.

  • Monday Little to no rainfall accumulation expected, with isolated totals up to 5 millimeters
  • Tuesday: Between 5-20 millimeters of rainfall across the country with areas across eastern and southern areas of Trinidad and Tobago receiving up to 25 millimeters. In isolated areas across the country, particularly western Trinidad, in heavy to violent showers and thunderstorms, localized totals may exceed 25 millimeters.
  • Wednesday: Between 5-20 millimeters of rainfall across the country with areas across eastern and southern areas of Trinidad and Tobago receiving up to 25 millimeters. In isolated areas across the country, particularly northwestern Trinidad, in heavy to violent showers and thunderstorms, localized totals may exceed 25 millimeters.
  • Thursday: Between 0-10 millimeters of rainfall across the country with areas across central and northern areas of Trinidad and Tobago receiving up to 20 millimeters. In isolated areas across the country, particularly across the northern half of Trinidad, in heavy to violent showers and thunderstorms, localized totals may exceed 25 millimeters.
  • Friday: Between 0-10 millimeters of rainfall across the country with areas across central and eastern areas of Trinidad and Tobago receiving up to 20 millimeters. Localized totals may exceed 25 millimeters.

As mentioned earlier, mainly from Tuesday, there is the possibility of street flooding and flash flooding and depending on where the rain falls, there is a very low chance of riverine flooding across Trinidad at this time.

Other Adverse Weather Impacts

Lightning: Lightning is possible in thunderstorm activity. Lightning can cause power outages, voltage dips, damage to life and property, particularly during cloud-to-ground lightning strikes.

Funnel Clouds and Waterspouts: Mainly on Thursday and Friday, with light winds, abundant heat, and forecast thunderstorms, funnel clouds across Trinidad will be possible with waterspouts in offshore, western coastal areas.

Why I May Not/Will Not See 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.

Through the forecast period, isolated to scattered rainfall is forecast.

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

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