Tropical Wave 23, ITCZ To Affect T&T Overnight Through Saturday

Tropical Wave 23 & The ITCZ Key Messages:
– The main hazard from the passage of this tropical wave and the ITCZ is locally heavy rainfall, mainly after midnight through Saturday afternoon. Generally, less than 15-25 millimeters are forecast across T&T, with isolated totals up to 75 millimeters in highly localized areas where thunderstorms or heavy showers occur.
Given that the latest modeling continues to show locally heavy rainfall, though mainly offshore. There is an elevated threat of street flooding and flash flooding, particularly across Trinidad. There is a negligible threat of riverine flooding.
– Seas are forecast to remain slight through Monday waves up to 1.25 meters in open waters east of T&T and near calm in sheltered areas. Note that in heavy showers or thunderstorms, seas may become locally rough and choppy.
— Gusty winds in excess of 55 KM/H are possible. Winds of this strength will produce wind damage including downed trees, utility poles, and roof damage. Localized power outages possible.

What We Know

A weak tropical wave, Tropical Wave 23, is forecast to bring enhanced convective activity as it interacts with the ITCZ across T&T. (Weathernerds)
A weak tropical wave, Tropical Wave 23, is forecast to bring enhanced convective activity as it interacts with the ITCZ across T&T. (Weathernerds)

The axis of Tropical Wave 23 is analyzed along 61W/62W, from 20N southward, moving westward at 10 to 15 knots. Widely scattered showers are moving across the Lesser Antilles and the adjacent Atlantic waters north through the northeast, otherwise, no significant convection is associated with this wave.

The wave is moving across the Lesser Antilles presently, dragging the ITCZ across Trinidad and Tobago.

Presently, deep tropical moisture is across Trinidad and Tobago, with near 0 wind shear across the country. Upper-level divergence and low-level convergence remain at neutral levels presently.

What We Forecast

While nearly all top models show the ITCZ producing a significant amount of precipitation after midnight through Saturday afternoon, widespread heat rainfall is not likely. This will be due to a dry-mid level environment and an unsupportive low-level atmosphere. Over the next 24 hours, between 25 to 75 millimeters of rainfall is possible, though higher accumulations are forecast to remain offshore.

Modelled rainfall outputs from top global models through the next 24 hours as of 8:00 PM Friday 17th July 2020. (Meteologix)
Modelled rainfall outputs from top global models through the next 24 hours as of 8:00 PM Friday 17th July 2020. (Meteologix)

Reiterating, a dry-mid level environment continues to plague the Eastern Caribbean, though abundant low-level and upper-level moisture is present. This may serve as the limiting factor for shower and thunderstorm development.

These models do bring winds between 30-45 KM/H and gusts in excess of 55 KM/H to Trinidad and Tobago, particularly during those heavier showers and thunderstorms.

Weather Forecast For T&T


Saturday: The ITCZ interacting with Tropical Wave 23 is forecast to be present across Trinidad and Tobago, with isolated showers and isolated thunderstorms forecast, with heavier activity remaining offshore. Activity is possible after midnight, peaking during the early morning, but precipitation chances on land during this time remain low as much of the activity forecast to remain offshore. By sunrise, a mostly sunny morning is forecast, with isolated shower and thunderstorm development across Trinidad after midday through late afternoon, favoring the Western half of Trinidad. Mostly settled conditions are forecast by the evening, with the odd isolated showers overnight.

Seas to remain slight, with waves up to 1.25 meters in open waters. In sheltered areas, near calm. Note that in heavier showers or thunderstorms, seas may become locally choppy or rough. Air quality to be at good levels.

The main hazards would be locally heavy rainfall, reducing visibility, and localized wind damage from wind gusts associated with heavier showers or thunderstorms. 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.


Sunday & Monday: As the ITCZ drifts southward, abundant moistre will remain across Trinidad and Tobago. Hence, across Trinidad and Tobago, isolated overnight showers are forecast to lead to a mostly settled morning, Isolated showers and thunderstorms are possible by the late morning through the afternoon, favoring Western areas of Trinidad. This will likely be triggered due to a combination of localized climatic effects. Conditions are forecast to settle by the evening into the night, with brisk, isolated showers possible.

The main hazards would be locally heavy rainfall, reducing visibility, and localized wind damage from wind gusts associated with heavier showers or thunderstorms. 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.

Seas to remain slight, with waves up to 1.25 meters in open waters. In sheltered areas, near calm. Note that in heavier showers or thunderstorms, seas may become locally choppy or rough. Air quality to be at good levels.

Impacts From Tropical Wave 23

As of Friday night, much of the heaviest rainfall is forecast to remain east of Trinidad and south of Tobago. However, locally heavy rainfall is possible, mainly across Trinidad on Saturday afternoon.

Wind

Peak sustained surface winds of 30 KM/H to 45 KM/H with gusts in excess of 55 KM/H are 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. Localized power outages expected.

High Wind Event Precautions
High Wind Event Precautions

Rainfall

Overall rainfall accumulations remain relatively low, but isolated totals may be high. Overall, less than 1 inch (25 mm) are forecast across Trinidad and Tobago. Isolated totals up to 2.5-3.0 inches (75 mm) are possible across Trinidad and Tobago, with heavier rainfall favoring Trinidad and offshore areas.

There is an elevated threat of street flooding and flash flooding. As of Friday night, there is a negligible threat of riverine flooding.

Thunderstorms and Lightning

With thunderstorms, locally severe wind (in excess of 55 KM/H), violent rainfall rates (in excess of 50 millimeters per hour) and lightning are all possible.

Gusty winds and lightning pose a threat to our power grid, causing localized power outages. Lightning may also strike trees, homes, or utility poles, causing damage to property. Lightning can also be deadly to persons outside during a thunderstorm.

But this model shows…

Individual model runs are just one possible outcome from a myriad of outcomes. Weather does not always follow what is modeled, and even what may be forecast. Beware of individual model runs being posted on social media.

Always check the National Hurricane Center for the latest information for tropical cyclones and your local meteorological offices for country-specific advisories.

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