No Significant Rainfall Forecast As Saharan Dust Diminishes Tropical Wave Impacts

Tropical Update Overview:
As of 2:00 AM, there are no areas being monitored in the Atlantic Basin for tropical cyclone formation.
Tropical Wave 6 – A weak tropical wave, hampered by significant Saharan Dust, is moving across T&T at this time. While few showers and the odd thunderstorm is possible, no significant rainfall is expected.
Tropical Wave 7 – Another weak tropical wave in the Central Tropical Atlantic, is forecast to move across T&T on Sunday into Monday, bringing isolated showers and thunderstorms.
Tropical Wave 8 – A tropical wave has just emerged off West Africa. It is too soon to tell what impacts, if any, this wave may bring as it traverses the region mid-next week.

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 mainly overnight into Thursday morning, Sunday afternoon into Monday, and possibly from Wednesday, though models disagree on the timing of arrival for Tropical Wave 08. While gusty winds may accompany heavier showers or thunderstorms, no significant weather impacts are forecast over the next 5 days.

Before we dive into the forecast and 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.

Tropical Wave 6

Tropical Wave 6 analyzed from 13N southward, along 61W, with scattered moderate convection and widespread cloudiness. Though most clouds are mid- and upper-level clouds, a few showers and isolated thunderstorms have developed near and over Trinidad. (Weathernerds)

As of 2:00 AM, the 6th tropical wave for the 2021 Atlantic Hurricane Season is located from 13N, along 61W, based on our analysis. The wave axis is moving westward around 10 to 15 knots (18 to 27KM/H). Creating fairly favorable upper-level conditions is an upper-level low-pressure system just east of the tropical wave.

Much of the cloud cover is associated with mid- to upper-level clouds across T&T and the Windward Islands. However, as this wave moves across T&T, scattered showers and brief, isolated thunderstorms are developing as previously forecast. However, there is moderate to strong wind shear and a notable amount of dry air at the mid-levels limiting precipitation.

Though cloudiness will persist through the first half of the day, with few showers and one or two more possible thunderstorms, dry air will become dominant again across T&T by the afternoon as a significant surge of Saharan Dust moves in.

Tropical Wave 7

Tropical Wave 7 is analyzed further east from 13N southward along 35W. (Weathernerds)
Tropical Wave 7 is analyzed further east from 13N southward along 35W. (Weathernerds)

As of 2:00 AM, the 7th tropical wave for the 2021 Atlantic Hurricane Season is located from 13N southward, along 35W, based on our analysis. The wave axis is moving westward around 10 to 15 knots (18 to 27KM/H).

This wave is forecast to move across the region on Sunday night into Monday morning, with moisture beginning to move across T&T from Sunday afternoon. Overall instability and moisture will be favorable for the development of cloudy weather, scattered showers, and isolated thunderstorms, mainly after sunset through Monday morning.

Atmospheric conditions are forecast to be marginally favorable through an 18-hour period for brisk heavy showers and thunderstorms. However, Saharan Dust and strong to very strong wind shear from the west will limit the strength of showers and thunderstorms, as well as keeping overall heavier rainfall totals east of T&T.

Tropical Wave 8

Tropical Wave 8 is analyzed further east from 18N southward along 20W. (Weathernerds)
Tropical Wave 8 is analyzed further east from 18N southward along 20W. (Weathernerds)

As of 2:00 AM, the 8th tropical wave for the 2021 Atlantic Hurricane Season is located from 18N southward, along 20W, based on our analysis. The wave axis is moving westward around 10 to 15 knots (18 to 27 KM/H) with numerous strong showers and isolated thunderstorms.

This wave recently emerged in the Atlantic Ocean, and model guidance shows the wave making its way across the Lesser Antilles during the middle of next week. However, it is too early to tell what impacts, if any, this wave may have on T&T. Notably, dense Saharan Dust will be present across the Atlantic as this wave moves westward.

Model guidance at this time showing moisture potentially affecting T&T from late Tuesday into Wednesday, though the axis moves across the Lesser Antilles Wednesday into Thursday.

The Forecast

At this time, there are no alerts, watches, or warnings issued for T&T from the Trinidad and Tobago Meteorological Service.

Thursday: Initially, mostly cloudy, dull, and windy conditions are forecast with brisk showers and isolated thunderstorms. By midday through the afternoon, a significant surge of Saharan Dust will regain dominance across the region, reducing air quality and visibility, leading to a hazy and dull night across T&T, barring the odd shower.

Friday: Mostly dull, hazy, and breezy conditions across Trinidad and Tobago, barring the odd isolated shower.

Saturday Mostly dull, hazy, and breezy conditions across Trinidad and Tobago, barring the odd isolated shower.

Sunday: Initially, similar conditions to the previous days with dull, hazy, and breezy conditions. From the afternoon, isolated showers are possible with partly to mostly cloudy periods. Cloudiness and showers will increase from nightfall into the overnight hours, with brief thunderstorm activity possible.

Monday: Initially, mostly cloudy to overcast skies with scattered showers and few heavy showers or isolated thunderstorms, remaining brisk. By midday through the afternoon, another significant surge of Saharan Dust will move in across the region, leading to a hazy and breezy afternoon into the night, barring the odd isolated shower.

Through the forecast period, Saharan Dust concentrations will be significant, particularly from Thursday through Saturday. Seas are forecast to remain moderate in open waters and less than 1.0 meters by choppy in sheltered areas. In heavy showers or thunderstorms, sheltered seas may become choppy.

Temperatures

Across both islands, overnight lows are forecast to be mild, with daytime highs warm.

The minimum low for Trinidad is forecast to be 23.0°C to 25.0°C. In Tobago, a minimum low between 24.0°C to 26.0°C is forecast. The maximum high for Trinidad and Tobago is forecast to be between 30.0°C and 32.0°C, higher across Trinidad.

Temperatures may record higher in urban and built-up areas, particularly between 9:00 AM and 3:00 PM. The maximum heat index in Trinidad is forecast to be between 35.0°C and 40.0°C while across Tobago between 33.0°C and 36.0°C.

Temperatures in cities, such as Port of Spain, tend to be much higher than surrounding locations due to a phenomenon called the Urban Heat Island Effect. There are several causes, but the main instigator for this phenomenon tends to be increased dark surfaces such as roads and pavement in cities, absorbing solar radiation more than surrounding areas.

Forecast Impacts

No significant rainfall is forecast over the next 5 days. However, gusty winds up to and in excess of 55 KM/H accompanying heavy showers or thunderstorms may cause power dips/outages, downed trees, and localized wind damage.

Winds

Sustained surface winds up to 35 KM/H. In shower activity, gusts up to and in excess of 55 KM/H are possible. 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.

Rainfall

Over the next five days, overall higher rainfall is forecast to favor eastern and southern Trinidad and Tobago, with accumulations less than 50 millimeters. However, localized totals in excess of 50 millimeters are possible in prolonged heavy showers or isolated thunderstorm activity. Note that highly isolated areas across Western areas of Trinidad may exceed daily forecast totals.

  • Thursday Less than 5 millimeters likely with isolated totals up to 15 millimeters possible.
  • Friday: Across the country, little to no rainfall is expected. In isolated areas, less than 5 millimeters are possible.
  • Saturday: Across the country, little to no rainfall is expected. In isolated areas, less than 10 millimeters are possible.
  • Sunday: Less than 10 millimeters across the country, with higher rainfall totals favoring southern and southwestern Trinidad.
  • Monday: Across the country, less than 10 millimeters. In isolated areas, up to 25 millimeters are possible, favoring southern and eastern halves of 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. However, no significant daily rainfall accumulations are forecast over the next 5 days.

Other 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.

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.

During the first half of Thursday, Sunday afternoon through Monday morning and next Wednesday through Thursday, isolated to scattered rainfall is expected. Outside of these periods, highly isolated rainfall is possible.

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

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