Periods of Showers, Thunderstorms Forecast Across T&T Due to ITCZ. Beginning of Multi-day Rain Event.

Key Messages:
— A tropical wave has moved across the Lesser Antilles presently. No widespread severe weather expected. The ITCZ is forecast to remain across the region into Friday, bringing a heavy rainfall threat.
— Through Friday, between 2 to 4 inches (50 to 100 millimeters) are possible across Trinidad and Tobago with isolated totals up to 5 inches (125 millimeters) across Eastern, Northern Trinidad and Tobago. There is an elevated threat of street flooding and flash flooding by the late week. There is the low chance of riverine flooding in the event of rainfall totals between 100-125 mm materializing, particularly across Northern and Eastern Trinidad.
— High tide at 1:36 PM may coincide with heavy showers in Port of Spain, resulting in slow runoff of possible flood waters.
— Seas will remain moderate, with waves between 1.5 meters and 2.0 meters are possible in open waters and choppy in sheltered areas. Swells are forecast to persist through Wednesday.
— Gusty winds in excess of 55 KM/H possible, particularly on Tuesday. Winds of this strength will produce wind damage including downed trees, utility poles and roof damage. Localized power outages possible.
— Landslides possible in elevated areas.

Trinidad and Tobago is NOT under any alerts, watches or warnings AT THIS TIME.

What We Know

A tropical wave located along 66W has dragged the ITCZ northward across Trinidad and Tobago, bringing showers and thunderstorms to the region. Additional showers and thunderstorms forecast to move across T&T through the next several days. Credit: Weathernerds
A tropical wave located along 66W has dragged the ITCZ northward across Trinidad and Tobago, bringing showers and thunderstorms to the region. Additional showers and thunderstorms forecast to move across T&T through the next several days. Credit: Weathernerds

As of 8:00 AM Tuesday, following the passage of the 53rd tropical wave of the 2019 Atlantic Hurricane Season, the ITCZ is now located directly across Trinidad and Tobago.

T&T is located in an area of favorable upper-level divergence and low-level convergence, with substantial coverage of heavy shower and thunderstorm activity.

Wind shear remains low, with a generally moist atmosphere. Mid-levels remain dry. Wind shear is forecast to remain low over the next 72 hours.

Isolated heavy showers and thunderstorms, with scattered light to moderate showers and increasing cloudiness, are moving across Trinidad and Tobago presently. The Northern and Eastern halves of Trinidad, in addition to Tobago, are experiencing the heaviest activity, and this is forecast to remain the case over the next 24-48 hours.

Impacts From The ITCZ

8:00 AM Tuesday 8th October 2019 Trinidad and Tobago Impact Assessment for the ITCZ across Trinidad and Tobago. Note that this will be continually updated.
8:00 AM Tuesday 8th October 2019 Trinidad and Tobago Impact Assessment for the ITCZ across Trinidad and Tobago. Note that this will be continually updated.

Weather

8:00 AM Tuesday 8th October 2019 forecast for Trinidad and Tobago.
8:00 AM Tuesday 8th October 2019 forecast for Trinidad and Tobago.

The forecast remains generally unchanged from Monday evening’s post.

Tuesday (until midnight); Tail end of Tropical Wave 53 & the ITCZ. Periods of showers and possible thunderstorms are likely across both Trinidad and Tobago, with the heaviest activity initially favoring the Northern and Eastern halves of Trinidad, gradually spreading across the remainder of the island, as well as Tobago. This activity will interrupt partly cloudy to mostly cloudy skies and will likely be accompanied by gusty winds. While conditions may become more settled by the late evening, lingering showers are likely into the night.

Wednesday (until midnight): The ITCZ. Similar conditions to Tuesday are forecast. Periods of showers and possible thunderstorms are likely across both islands, with heavier showers and thunderstorms now favoring the Western and Northern halves of Trinidad. Conditions are forecast to become settled into the night, with a few lingering showers.

Thursday (until midnight): The ITCZ and a low-level trough. Essentially the same forecast as the two previous days. Periods of showers and thunderstorms forecast, interrupting partly cloudy to mostly cloudy skies. Conditions become settled by the late evening with a few lingering showers. Elevated threat for flooding.

Friday (until midnight): The ITCZ, upper and low-level trough. Periods of showers and thunderstorms for the 4th day in a row, interrupting partly cloudy to mostly cloudy skies. Conditions become settled by the late evening with a few lingering showers. Elevated threat of flooding.

Wind

Peak sustained surface winds of 25 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, particularly on Tuesday through Wednesday morning during heavy shower or thunderstorm activity.

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

Through Friday, between 2 to 4 inches (50 to 100 millimeters) are possible across Trinidad and Tobago with isolated totals up to 5 inches (125 millimeters) across Eastern, Northern Trinidad and Tobago.

There is an elevated threat of street flooding and flash flooding by the late week. There is a very low chance of riverine flooding in the event of rainfall totals between 100-125 mm materializing, particularly across Northern and Eastern Trinidad.

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.

Seas and Surf

Long-period swells are forecast to continue through Wednesday, with seas moderate in open waters with waves between 1.5 to 2.0 meters. In sheltered areas, seas are near 1.0 meters, but choppy, particularly during heavier showers or thunderstorms.

What’s Next?

The axis of the tropical wave is already west of Trinidad and Tobago. However, the Intertropical Convergence Zone is forecast to linger through Friday. Saharan Dust is forecast to be on the decline, although moderate air quality is ongoing.

Why I May Not/Will Not See Constant Rainfall?

Tropical waves typically have fair weather ahead of the wave axis, though other features in the area such as surface troughs, increased atmospheric moisture, and local climatic effects, to name a few, may trigger showers and the odd thunderstorm. Following the passage of the wave, much of the active weather typically associated with a tropical wave occurs.
Tropical waves typically have fair weather ahead of the wave axis, though other features in the area such as surface troughs, increased atmospheric moisture, and local climatic effects, to name a few, may trigger showers and the odd thunderstorm. Following the passage of the wave, much of the active weather typically associated with a tropical wave occurs.

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.

Generally, because of winds associated with tropical waves, showers and thunderstorms tend to follow a west-northwest track, generally missing areas across Southwestern Trinidad and even Northwestern Trinidad – though activity due to local climatic effects such as daytime heating may trigger shower and thunderstorm development across these areas. See the below graphic for a simple explanation.

With the ITCZ, mostly isolated to scattered showers forecast. Hence, we are likely to see intermittent showers and thunderstorms, interrupting partly cloudy to overcast skies throughout the week.

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