Tropical Update: Invest 96L, 3 Tropical Waves East of T&T

Tropical Update Overview:
West Atlantic Area of Interest – An area of low pressure is forecast to form southeast of the United States later this week, with low chances of tropical cyclone formation as of Sunday afternoon.
Tropical Wave 16 – A weak, not well defined tropical wave is forecast to merge with Tropical Wave 17, with the merged wave moving across T&T on Tuesday into Wednesday, bringing elevated chances for showers and thunderstorm activity.
Tropical Wave 17/INVEST 96L – A well-defined tropical wave is forecast to merge with Tropical Wave 16. A low-pressure area along the northern wave axis is being monitored for tropical development, with low chances over the next 48 hours to 5 days. While much of the active weather associated with the merged wave and INVEST 96L is forecast to remain north of T&T, showers and isolated thunderstorms are possible Tuesday into Wednesday. Increased winds and Saharan Dust will follow the wave axis on Thursday.
Tropical Wave 18 – A tropical wave has just emerged in the Atlantic Ocean. This wave is forecast to move across the Lesser Antilles in 7-8 days. It is too soon to tell, if any, impacts to the area but it is not being monitored for development at this time.

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. The passage of Tropical Wave 16/17 is forecast to bring isolated to scattered showers and isolated thunderstorms Tuesday into Wednesday. The main hazards include locally heavy rainfall and gusty winds up to and in excess of 60 KM/H. Street flooding is possible, with flash flooding lesser so. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage

Before we dive into the 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.

You can read more about the weather associated with Tropical Waves, as well as what to expect as these waves move through the region below.

West Atlantic Area of Interest

The area being monitored for the development of a low-pressure system over the next 5 days for tropical development. (NHC)
The area being monitored for the development of a low-pressure system over the next 5 days for tropical development. (NHC)

As of the 5:00 PM Tropical Update, the National Hurricane Center is monitoring an area off the Eastern United States’ coast for development.

According to the NHC’s 2:00 PM Tropical Weather Outlook, “A low-pressure area is expected to form in a couple of days off of the southeastern coast of the United States. Some additional development of this system could then occur as it moves generally northeastward.”

The NHC has given this area a near zero (0%) chance of tropical cyclone formation over the next 48 hours and a 20% chance of tropical cyclone formation over the next 5 days.

Overall model support has decreased over the last few runs, with 50% European ensemble (EPS) models showing winds of tropical depression strength possible over the next 72 hours, with less than 10% showing winds of tropical storm strength. There is even less support from the American (GFS) model, and no support from the U.K. (UKMET) model.

Hence, it won’t be surprising to see chances dwindle further in the NHC’s 7 PM EST Tropical Weather Outlook. Regardless of formation, this system will not pose any threat to the Lesser Antilles, including Trinidad and Tobago.

Tropical Wave 16

Tropical Wave 16 is analyzed along 50W, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms, generally embedded within the ITCZ (Weathernerds)
Tropical Wave 16 is analyzed along 50W, producing cloudiness and isolated to scattered showers, as well as isolated thunderstorms, generally embedded within the ITCZ (Weathernerds)

As of the 5:00 PM Tropical Update, the 16th tropical wave for the 2020 Atlantic Hurricane Season is located along 50W, from 13N southward based on our analysis. The wave axis is moving westward around 15-20 knots (28-37 KM/H).

Much of the activity associated with this wave is embedded within the ITCZ, with a large moisture plume surrounding the wave axis. Weak troughing is evident at the surface with this wave north of 13N.

Models continue to show that this wave and its associated moisture will merge with (or have a very little distinction from) Tropical Wave 17 as it moves westward. Moisture associated with the merged waves will begin to affect T&T after midnight Monday through early Thursday.

Tropical Wave 17 & INVEST 96L

Tropical Weather Outlook from the National Hurricane Center as of 2:00 PM Sunday 28th June 2020 (NHC)
Tropical Weather Outlook from the National Hurricane Center as of 2:00 PM Sunday 28th June 2020 (NHC)

As of the 5:00 PM Tropical Update, further east, the axis of Tropical Wave 17 is approximately along 40W to 45W from 21N southward, moving west at 15-20 knots (28-37 KM/H).

Across the northern area of the wave axis, a 1009 millibar low pressure is being monitored for development by the National Hurricane Center, giving it a low (10%) chance for tropical cyclone formation over the next 48 hours and a low (20%) chance for tropical cyclone formation over the next five days as it rapidly moves west-northwest at 20 knots (37 KM/H).

This tropical disturbance has been dubbed as INVEST 96L. An INVEST (short for investigative area, also called area of interest) is a designated area of disturbed weather that is being monitored for potential tropical cyclone formation.

According to the NHC’s 2:00 PM Tropical Weather Outlook, “A tropical wave located several hundred miles west-southwest of the Cabo Verde Islands is moving west-northwestward at about 20 mph. Some slow development of this system is possible during the next 2 to 3 days. After that time, environmental conditions are forecast to become less conducive for development.”

Presently, this wave has somewhat favorable upper-level divergence, marginally favorable low-level convergence, and an abundant moisture envelope.

European (EPS) Model probability of winds of Tropical Depression strength over the next 72 hours (Weathermodels)
European (EPS) Model probability of winds of Tropical Depression strength over the next 72 hours (Weathermodels)

Model guidance from the top three models for tropical cyclone development (EMCWF, GFS, UKMET) does not develop this system. Only the ensemble runs European (EPS) model, less than 40%, show winds of tropical depression strength possible over the next 72 hours, with less than 5% showing winds of tropical storm strength.

Intensity models all keep this as a weak low-pressure system through the next 24-48 hours before ceasing tracking. Regardless of formation, any adverse impacts associated with this area of the tropical wave will move north of T&T.

However, the southern half of the wave axis is forecast to merge with Tropical Wave 16. The merged wave is forecast to move across Trinidad and Tobago, bringing the ITCZ across the islands beginning late Tuesday through Wednesday. The highest chances for locally heavy rainfall, as of Sunday evening, is forecast on Tuesday.

In showers and thunderstorms, stronger winds may mix down to the surface, producing downbursts and areas of wind damage.

Tropical Wave 18

Tropical Wave 18 in the Eastern Atlantic Ocean. (Weathernerds)
Tropical Wave 18 in the Eastern Atlantic Ocean. (Weathernerds)

As of the 5:00 PM Tropical Update, further east, the axis of Tropical Wave 18 is approximately at 20W to 22W from 15N southward, moving west at 15 knots (27 KM/H). This tropical wave is embedded within the ITCZ.

This tropical wave is forecast to move across the entire Lesser Antilles in 7-8 days based on model guidance. It is too soon to tell, if any, impacts to the area but it is not being monitored for development at this time.

What does all of this mean for Trinidad and Tobago?

Monday: A few early morning showers are forecast to give way to a mostly sunny and somewhat hazy day. Partly cloudy skies are possible by the mid to late morning, with brisk, isolated showers favoring Trinidad through the afternoon. Conditions are forecast to remain settled until midnight, where isolated showers and increasing cloudiness is forecast.

Seas to remain moderate, with waves near 1.5 meters in open waters, occasionally up to 2.0 meters. In sheltered areas, less than 1.0 meter. No adverse weather impacts forecast, though air quality will be at moderate, improving by nightfall into Tuesday.


Tuesday: Moisture associated with the ITCZ and the merged Tropical wave 16/17 will begin to move across T&T. After midday, isolated to scattered showers and isolated thunderstorms are forecast to favor Eastern and Southern Trinidad, gradually moving west to west-northwest. These conditions, mainly isolated to scattered showers, are forecast throughout the day, interrupting partly to mostly cloudy skies.

Overall, heavier showers and thunderstorms are forecast to favor southeastern Trinidad and offshore areas. 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 in areas where more prolonged heavy rainfall may occur.

Gusty winds, up to and in excess of 60 KM/H possible. Seas to remain moderate, with waves up to 1.5 meters in open waters, occasionally up to 2.0 meters. In sheltered areas, near 1.0 meter but choppy due in heavier showers or thunderstorms.



Wednesday: Moisture associated with the merged Tropical Wave 16/17 will continue to move across the region, gradually diminishing by the late night. Isolated showers and isolated thunderstorms are forecast across both islands, with heavier activity continuing to favor Western and hilly areas. after an initially settled morning. Activity is not forecast to be as scattered as Tuesday at this time. Conditions are forecast to settle by the late afternoon. The tropical wave will drag the ITCZ across Trinidad, aiding the development of thunderstorm activity, mainly south of the island. The approaching high-pressure system forecast to push the ITCZ southward on Thursday.

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 in areas where more prolonged heavy rainfall may occur.

Gusty winds, up to and in excess of 60 KM/H possible. Seas to remain moderate, with waves up to 1.5 meters in open waters, occasionally up to 2.0 meters. In sheltered areas, near 1.0 meter but choppy due in heavier showers or thunderstorms. Air quality forecast to diminish by nightfall into Thursday as a surge of Saharan Dust returns.


Thursday: Across the northern half of Trinidad and Tobago, a mostly hazy and partly cloudy day is forecast, with isolated afternoon showers possible, generally remaining light. This is due to a high-pressure system, bringing increased Saharan Dust concentrations and breezy conditions, dominating across Trinidad and Tobago. Across Northern Trinidad and Tobago, the main hazard continue to be reduced air quality, visibility.

Across Southern Trinidad, at times across Central Trinidad, the ITCZ is forecast to linger across the area, triggering heavier showers and even thunderstorms during the afternoon through early Friday morning. Gusty winds, frequent lightning (in thunderstorm activity) and locally heavy rainfall possible.

Gusty winds, up to 60 KM/H possible. Seas to remain moderate, with waves up to 2.5 meters in open waters. In sheltered areas, near 1.0 meter. Air quality forecast to diminish.


Friday: Similar conditions to Thursday are forecast with a few overnight showers, isolated thunderstorms favoring Southern Trinidad forecast into the early morning. A high-pressure system, with increased Saharan Dust concentrations and breezy conditions, will dominate across Trinidad and Tobago. A mostly dull and hazy day is forecast, with brisk isolated showers possible. The main hazards continue to be reduced air quality, visibility across Northern Trinidad and Tobago, while across Central and Southern Trinidad, gusty winds accompanying showers or thunderstorms, locally heavy rainfall and possible frequent lightning.

Gusty winds, up to 60 KM/H possible. Seas to remain moderate, with waves up to 2.5 meters in open waters. In sheltered areas, near 1.0 meter. Air quality forecast to slightly improve.


Possible Impacts This Week

Winds: Sustained surface winds between 35 KM/H and 50 KM/H are forecast by the later end of the week, with gusts up to and in excess of 60 KM/H possible in heavy showers or thunderstorms across Trinidad and Tobago, particularly on Tuesday and Wednesday.

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.

High Wind Event Precautions
High Wind Event Precautions

Rainfall

Monday: Little overall rainfall accumulations forecast, with isolated totals up to 5 millimeters in areas that experience isolated heavy showers.

Tuesday: Less than 5-15 millimeters across both islands, with isolated totals up to 45 millimeters, particularly across Trinidad in areas that experience heavy downpours and localized thunderstorms, favoring Eastern Trinidad.

Wednesday: Less than 5-15 millimeters across both islands, with isolated totals up to 25 millimeters, particularly across Trinidad in areas that experience heavy downpours and localized thunderstorms.

Thursday: Little overall rainfall accumulations forecast, with isolated totals up to 15 millimeters in areas that experience isolated heavy showers and thunderstorms.

Friday: Little overall rainfall accumulations forecast, with isolated totals up to 15 millimeters in areas that experience isolated heavy showers. and 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 in areas where more prolonged heavy rainfall may occur.

Frequent Lightning: In addition, with forecast thunderstorms, frequent lightning is likely. 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 Constant 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.

Isolated to scattered activity is forecast on Tuesday, with an isolated activity forecast on Wednesday. Highly isolated activity forecast on Monday, Thursday, and Friday.

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

Tropical Cyclone Climatology

Tropical Cyclone Points of Origin during the last week of June and first week of July July. Though much of the points of origin are west or north of T&T as we move through the first into the second month of the Hurricane Season, we still need to pay attention to some of these waves and the ITCZ, which have historically brought major flooding events to T&T, hence all low-pressure systems in the Atlantic should be closely monitored, as we do in the Tropical Update.

List of names for the 2020 Atlantic Hurricane Season, which will be updated each tropical update as new systems develop.
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