Tropical Wave 11: No Direct Tropical Threat To T&T, Forecast To Bring Heavy 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 Tuesday, it has low (30%) 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 on Tuesday.
— 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. Severe thunderstorms are possible on Thursday.
— An Adverse Weather Alert #2 is in effect for Trinidad and Tobago from 3:30 PM Tuesday through 5:00 PM Wednesday from the Trinidad and Tobago Meteorological Service at this time.

The Tropical Outlook

Tropical Weather Outlook as of 8:00 AM Tuesday 22nd June 2021.

The National Hurricane Center (NHC) is monitoring a well-defined tropical wave (Tropical Wave 11), approximately 1,000 kilometers east of Trinidad and Tobago. Showers and thunderstorms have increased over the last several hours. 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 to 20 MPH (24 KM/H to 32 KM/H). As of 8:00 AM Tuesday 22nd June 2021, the NHC has given this tropical disturbance a low (30%) chance of tropical cyclone formation over the next 48 hours and five days respectively. Presently, thunderstorms and showers are producing winds between 40 KM/H to 65 KM/H.

Top global models show Tropical Wave 11 moving west through the next 48 hours while the area of low-pressure splits from the wave and moves more west-northwest by the end of the week. However, troughing will remain across the area in the vicinity of 50W, indicating Tropical Wave 12 catching up to the area and eventually moving across the Windwards later this week.

00Z June 22nd, 2021 EMCWF maximum wind gusts over the next 5 days showing an 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 22nd, 2021 EMCWF maximum wind gusts over the next 5 days showing an 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 remain 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 less than 50% of its runs reaching past tropical-depression-strength (20+ knots or 37 KM/H sustained winds) and none reaching tropical-storm-strength (34+ knots or 63 KM/H sustained winds). The ensemble runs have the center of this disturbance passing across Barbados, with a spread as far south as T&T to as north as Guadeloupe.

We’re also monitoring Tropical Wave 13, which models indicate some development is possible over the weekend into next week as it moves into and across the Atlantic. It is too soon to tell what impacts, if any, this system may have to the Lesser Antilles.

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)

Tuesday: A partly to mostly cloudy day is forecast across T&T, with brief sunny spells during the mid-morning across northwestern and western areas of Trinidad. By the late morning through the afternoon, periods of rain, scattered showers, some becoming heavy, and scattered thunderstorms are forecast to interrupt cloudy skies. Heavier rainfall is forecast to remain across southern and eastern Trinidad initially. Rainfall will continue into and through the night.

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 late afternoon into evening, with a resurgence in showers and isolated thunderstorms near and after midnight favoring northern Trinidad and Tobago.

Thursday: Early morning showers and thunderstorms favoring northern Trinidad and Tobago will spread across the country, subsiding shortly after daybreak and lead to a partly cloudy and hot day, with little to no wind. Severe thunderstorms are forecast to develop by the late morning through the afternoon, favoring central and northern Trinidad. Heavy to torrential rainfall, gusty winds, and funnel clouds are possible. Showers and thunderstorms will gradually lift northward, with mostly hot and sunny conditions across the southern half of the country leading to a mostly settled night.

Friday: Isolated early morning showers are forecast to continue through the morning, with partly cloudy and hot conditions with little to no winds. By the late morning through the afternoon, scattered showers and isolated strong thunderstorms are forecast to develop across the western half of Trinidad, spreading across the island with isolated showers across Tobago. Conditions are forecast to settle into the evening, with a resurgence of showers forecast near midnight across the country.

Saturday: Partly to mostly cloudy conditions with isolated to scattered showers across the country. A few showers may become heavy, favoring Trinidad by the late morning through the afternoon. Isolated showers to continue into the night.

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 broad area of showers and thunderstorms. This wave is forecast to split into two, with the southern half of the wave axis moving 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 later into the week, 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 Friday 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 and waterspout development, particularly on Thursday.

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 mostly cloudy to overcast days, 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. Severe thunderstorms are forecast on Thursday.

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, the forecast overall rainfall accumulations have increased. rainfall accumulations between 25-75 millimeters are forecast, with higher totals up to 100 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.

  • Tuesday: Between 5-25 millimeters of rainfall across the country with areas across eastern and southern areas of Trinidad and Tobago receiving up to 40 millimeters. In isolated areas across the country, particularly western Trinidad, in heavy to violent showers and thunderstorms, localized totals may exceed 40 millimeters.
  • Wednesday: Between 5-20 millimeters of rainfall across the country. In isolated areas across the country, particularly southwestern, northern, and eastern Trinidad as well as eastern Tobago, in heavy to violent showers and thunderstorms, localized totals may exceed 20 millimeters.
  • Thursday: Up to 10 millimeters of rainfall across the southern half of Trinidad and across Tobago. Across the northern half of Trinidad, rainfall totals up to 45 millimeters are possible, with isolated higher amounts.
  • Friday: Between 0-10 millimeters of rainfall across the country with isolated areas receiving up to 20 millimeters. Localized totals may exceed 25 millimeters.
  • Saturday: Between 0-10 millimeters of rainfall across the country with isolated areas 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.

Severe thunderstorms: As mentioned earlier, severe thunderstorms are possible on Thursday across the northern half of Trinidad, and strong thunderstorms are forecast on Friday across western areas. These stronger thunderstorms bring the elevated threat of torrential rainfall rates, gusty winds in excess of 60 KM/H, and in rare instances, funnel clouds, tornadoes, and hail. These threats are on the table mainly on Thursday.

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?

Facebook Comments