Invest 92L To Bring Inclement Weather To T&T, Lesser Antilles

INVEST 92L Key Messages:
Watches & Warnings: An Adverse Weather Alert (Yellow Level) was issued at 6:51 AM for T&T, which went into effect at 7:00 AM through 6:00 PM. Given that the center (and strongest winds) of this system is forecast to move across the Leewards, well north of T&T, tropical storm watches/warnings may be issued for those islands later today.
– Track: The track of INVEST 92L stays well north of T&T. The core of INVEST 92L is forecast to track across the Leeward Islands. Peak activity across is expected on Tuesday through early Thursday.
– Intensity: iNVEST 92’s large size, multiple low-level circulations, and struggle with dry air will inhibit any rapid development or intensification. However, a tropical storm is likely to form over the next 48 hours and 5 days respectively, due to high chances for formation from the National Hurricane Center as of 2:00 AM Tuesday.

Key Messages for INVEST 92L as of 5:00 AM Tuesday 28th July 2020 for Trinidad and Tobago
Key Messages for INVEST 92L as of 5:00 AM Tuesday 28th July 2020 for Trinidad and Tobago

Rainfall: The rainfall forecast is elevated. Across Trinidad and
Tobago, between 50-100 mm of rainfall possible between Tuesday through Friday. Isolated totals in excess of 150 mm possible.
– Flooding: Street flooding and flash flooding in heavy to violent showers and thunderstorms are likely across both islands. There is a very low to low chance of riverine flooding across Trinidad.
– Landslides: There is a high risk of landslides across both islands
– Seas: Seas, mainly on Tuesday through Tuesday, forecast to be moderate to rough, with waves up to 2.5 meters, occasionally up to 3.0 meters in open waters, mainly east of Trinidad and in Tobago’s coastal waters. In sheltered areas, up to 1.0 meters and choppy.
– Winds: Gusty winds in excess of 65 KM/H are possible across T&T in the event of showers/thunderstorms. Winds of this strength will produce wind damage including downed trees, utility poles, and roof damage. Power outages possible.

NHC: Tropical Storm Watches/Warnings Possible For Leewards Later Today

Tropical Weather Outlook from the National Hurricane Center as of 2:00 AM AST Tuesday 28th July 2020
Tropical Weather Outlook from the National Hurricane Center as of 2:00 AM AST Tuesday 28th July 2020

The National Hurricane Center, as of 5:00 AM, continues to monitor a tropical disturbance, INVEST 92L east of the Lesser Antilles..

Based on the latest Tropical Weather Outlook from the National Hurricane Center, “Shower activity associated with a low-pressure area located about 750 miles east of the Windward Islands is gradually increasing in organization. However, recent satellite-derived wind data indicate that the circulation remains broad and elongated, and the low does not yet have a well-defined center of circulation. Environmental conditions are expected to become somewhat more conducive for development, and a tropical depression or tropical storm is likely to form during the next couple of days while the system moves west-northwestward at 15 to 20 MPH and approaches the Leeward Islands. Regardless of development, locally heavy rains and gusty winds are likely across portions of the Leeward Islands on Wednesday and will spread westward to the Virgin Islands and Puerto Rico Wednesday night and Thursday. Interests on these islands should continue to monitor the progress of this system, and tropical storm watches or warnings could be required for portions of the area later today.

Watches & Warnings

As of 5:00 AM Tuesday 28th July 2020, there are no tropical storm watches or warnings in effect for any islands of the Lesser Antilles.


At 6:51 AM, the Trinidad and Tobago Meteorological Service issued an Adverse Weather Alert (Yellow Level) for T&T, which went into effect at 7:00 AM through 6:00 PM Tuesday.

Why No Tropical Storm Warning for Trinidad and Tobago?

A Tropical Storm Watch will be issued in conjunction with the National Hurricane Center and your local meteorological agency if tropical storm conditions (sustained winds of 39 to 73 MPH, or 63 to 118 KM/H) are possible within the specified area within 48 hours.

A Tropical Storm Warning will be issued in conjunction with the National Hurricane Center and your local meteorological agency if tropical storm conditions (sustained winds of 39 to 73 MPH, or 63 to 118 KM/H) are expected within the specified area within 36 hours.

Given that these conditions will not be likely for T&T, as strongest winds are forecast to track across the Leewards, there will be no such watches or warnings for our country.

The main hazard for Trinidad and Tobago, is heavy, flooding rainfall.

What We Know

INVEST 92L in the Central Atlantic, producing a large and scattered area of moderate to strong convection as of the morning of Tuesday 28th July 2020. (Weathernerds)
INVEST 92L in the Central Atlantic, producing a large and scattered area of moderate to strong convection as of the morning of Tuesday 28th July 2020. (Weathernerds)

INVEST 92L continues to show signs of organization as it nears the Lesser Antilles, with moderate to strong showers and thunderstorms occuring just east of Trinidad and Tobago, though the center of circulation remains well to the northeast.

This tropical disturbance is a highly tilted southwest to northeast Tropical Wave, extending approximately 2,000 kilometers wide. Near the center of circulation, there is favorable low wind shear, but unfavorable wind shear exists, extending across the northwest and southeast.

Highly favorable upper–level divergence and low-level convergence exist mainly across the southern half of this disturbance, enhancing convective activity that approaches T&T. The cyclonic spin (vorticity) is also over this region, remaining elongated and quite broad, extending from the north coast of South America to 45W.

This tropical wave/tropical disturbance has been interacting with the Intertropical Convergence Zone, dragging it northward. Activity with the ITCZ tends to peak between midnight and 6:00 AM and again during the afternoon, between 12:00 PM and 3:00 PM.

If this system forms, the next name on the list of names for the 2020 Atlantic Hurricane Season is Isaias. The current record for the earliest ‘I’ storm in the Atlantic basin is Irene on August 7, 2005.

Regardless of formation, peripheral impacts are forecast for T&T, with the main hazard being heavy showers and thunderstorms bringing heavy rainfall to both islands beginning Tuesday, mainly through Thursday.

What We Forecast

Track

Center of circulation moves across Leewards, peripheral impacts across the entire Lesser Antilles.

Early-cycle track guidance from top models, for INVEST 92L as of 00Z Tuesday 28th July 2020. (NCAR)
Early-cycle track guidance from top models, for INVEST 92L as of 00Z Tuesday 28th July 2020. (NCAR)

Based on present model guidance, the core (i.e., where the heaviest showers and thunderstorms may occur) is forecast to move across the Leeward Islands. This general track has held consistent over the last several model runs, though models have struggled to grapple with the multiple low-level centers.

Regardless of track, the circulation of this system is large, nearly 800 kilometers in diameter, with the wave axis nearly 2,000 kilometers in length. Because of this, rainfall impacts are forecast across the entire Lesser Antilles, while stronger winds are forecast to impact the Leewards and Greater Antilles.

Intensity

A large but weak tropical storm moving across the Leewards

Early-cycle intensity guidance from top models, for INVEST 92L as of 00Z Tuesday 28th July 2020. (NCAR)
Early-cycle intensity guidance from top models, for INVEST 92L as of 00Z Tuesday 28th July 2020. (NCAR)

Although there has been a recent increase in deep convection in association with INVEST 92L, ASCAT and satellite data continues to show a broad and elongated area of rotation.

This particularly large tropical disturbance has been to its detriment, as it takes time for larger rotations to consolidate and form an organized tropical cyclone.

Significant Saharan Dust remains across the northern half of the disturbance, likely inhibiting convection over the area, where the strongest winds exist. It is also moving to the west-northwestward quickly, between 15-20 MPH.

However, with a large, rotating system like INVEST 92L, the eventual formation of a tropical cyclone is likely. Most top models bring this system to tropical storm strength within 36 hours, with very few bringing this to hurricane strength later in the forecast period.

Forecast for T&T

Tuesday: Winds will be from the east to northeast, resulting in shower and thunderstorm activity moving from the northeast to southwest, instead of the usual east to west. Activity ahead of Invest 92L will begin to affect Tobago during the mid to late morning, while across Trinidad by the late morning through the afternoon. After an initially sunny to a partly cloudy morning, isolated to scattered showers and isolated thunderstorms are forecast to affect Trinidad and Tobago, with periods of rain. The heaviest activity forecast to occur during the afternoon. The activity forecast to be enhanced along Western areas of Trinidad due to a combination of localized climatic effects such as daytime heating and sea breeze convergence. Isolated showers and thunderstorms are forecast into the night, with nearly calm winds.

Conditions are forecast to mostly settle by the evening, with lingering isolated showers and thunderstorms, generally remaining offshore initially.

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. Landslides are also possible in elevated areas of both islands, particularly where heavy rainfall occurs.

Seas to remain moderate, with waves up to 2.0 meters in open waters. In sheltered areas, less than 1.0 meter. Note that in heavier showers or thunderstorms, seas may become locally choppy or rough. Air quality to be at good levels.



Wednesday: As INVEST 92L moves to our north, winds are forecast to move from near calm to light but from the south. This will result in showers and thunderstorm activity moving from the south to the north, instead of the usual east to west.

Isolated to scattered showers and isolated thunderstorms are forecast after midnight, with isolated activity persisting through the morning. As showers and thunderstorms move across the Northern Range of Trinidad and Main Ridge of Tobago from the south, orographic enhancement is possible, setting up a heavy rainfall threat along the southward facing slopes, meaning the East-West Corridor in Trinidad and all areas of Tobago (due to the island’s small size).

Isolated to scattered showers and thunderstorms are forecast to persist into the night, mainly across Trinidad.

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. Landslides are also possible in elevated areas of both islands, particularly where heavy rainfall occurs.

Seas to remain moderate, occasionally rough, with waves up to 2.5 meters, occasionally up to 3.0 meters in open waters. In sheltered areas, near 1.0 meter. Note that in heavier showers or thunderstorms, seas may become locally choppy or rough. Air quality to be at good levels.


Thursday into Friday: As INVEST 92L, or its eventual tropical cyclone moves to the north and west, winds will continue to move from the south to southeast, moving deep tropical moisture across the islands. Conditions are forecast to be slightly drier, so shower and thunderstorm activity will favor the late mornings through the afternoon, generally interrupting sunny to partly cloudy skies.

As showers and thunderstorms move across the Northern Range of Trinidad and Main Ridge of Tobago from the south, orographic enhancement is possible, setting up a heavy rainfall threat along the southward facing slopes, meaning the East-West Corridor in Trinidad and all areas of Tobago (due to the island’s small size).

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. Landslides are also possible in elevated areas of both islands, particularly where heavy rainfall occurs. Depending on overall rainfall totals, there may be a very low to low risk of riverine flooding by Thursday.

Seas are forecast to settle, with waves moderate (up to 2.0 meters) on Thursday and moderate to slight on Friday (up to 1.5 meters). In sheltered areas, near to below 1.0 meter. 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 28

For Trinidad and Tobago, the main hazard is heavy rainfall causing flooding and landslides, with gusty winds also a localized concern, as well as rough seas.

Wind

Across Trinidad and Tobago, wind gusts in excess of 65 KM/H are possible in heavier showers or thunderstorms.

With wind gusts in excess of 65 KM/H, whole trees are expected to be in motion, with tree damage likely. 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. Power outages expected, with damage to trees, power lines and small structures possible.

High Wind Event Precautions
High Wind Event Precautions

Rainfall

Overall rainfall accumulations are elevated through Thursday. Generally, between 50-100 millimeters of rainfall forecast Tuesday through early Friday, with isolated totals in excess of 150 millimeters in areas of persisting heavy rainfall and thunderstorm activity possible.

Street flooding and flash flooding in heavy to violent showers and thunderstorms are likely across both islands. There is a very low to low chance of riverine flooding across Trinidad. There is a high risk of landslides across both islands

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

Seas, mainly on Wednesday, forecast to be moderate to rough, with waves occasionally up to 3.0 meters in open waters. In sheltered areas, up to 1.0 meters and choppy.

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