Invest 93L: What you need to know

Tropical Wave 55/Invest 93L Key Messages:
– Tropical Wave 55/Invest 93L has low chances of development over the next 5 days as it moves west-northwest towards the central Lesser Antilles.
Track: Forecast models take the core of this system north of Trinidad and Tobago, tracking near and north of Barbados and across the French Antilles.
Intensity: No operational, top models develop this system into an organized tropical cyclone over the next 5 days.
Impacts: Scattered showers and thunderstorms, accompanied by gusty winds, are possible across Barbados, Trinidad, and Tobago from late Monday. Similar conditions are forecast to spread northward across the remainder of the central and northern Lesser Antilles and Leewards by Tuesday night through Wednesday.

Tropical Wave 55 (Invest 93L) in the Eastern Atlantic is producing some disorganized showers and thunderstorms 800 kilometers east-northeast of Trinidad and Tobago as of 2:00 AM Monday 11th October 2021. This tropical disturbance is forecast to move across the Lesser Antilles over the next 2-3 days, with deep tropical moisture and all the ingredients for unsettled weather. However, it is unlikely this system forms into an organized tropical cyclone before moving across the Lesser Antilles.

The Latest Information From The National Hurricane Center

Invest 93L’s Tropical Weather Outlook as of 8:00 PM Sunday 10th October 2021. (National Hurricane Center)

Tropical Wave 55 (or Invest 93L) remains disorganized east of Trinidad and Tobago as Monday morning. Based on the latest information from the National Hurricane Center, the center of Invest 93L was located near 11.1°N, 52.4°W, approximately 800 kilometers east-northeast of Trinidad and Tobago.

Environmental conditions are forecast to become marginally conducive for limited development over the next day or so as Invest 93L moves west-northwest near 24 KM/H. However, strong upper-level winds are forecast to limit further development as it moves across the Lesser Antilles.

The disturbance is forecast to approach the central and northern Lesser Antilles by late Monday and early Tuesday. Regardless of development, the system could produce locally heavy rainfall and gusty winds across portions of the central and northern Lesser Antilles on Tuesday and across the Virgin Islands and the Leeward Islands on Wednesday.

Invest 93L east of the Lesser Antilles in the Atlantic Ocean. (Weathernerds)

Over the last 24 hours, pulses of convection have been noted mainly north of the system’s circulation.

Presently, Invest 93L is located in an area with warm sea surface temperatures between 28°C and 29°C, but strong wind shear from the west to northwest, and marginally favorable upper-level divergence.

Where is Invest 93L Going?

The takeaway: Forecast models take the core of this system north of Trinidad and Tobago, tracking near and north of Barbados and across the French Antilles. Everyone in the Lesser Antilles should monitor this system, but those in the Northern Windwards and Leewards should pay close attention to the eventual forecast track. This system poses no direct threat to Trinidad and Tobago at this time.

Invest 93L's forecast tracks from top dynamical and consensus hurricane models as of 2:00 AM Monday 11th October 2021. (NCAR)
Invest 93L’s forecast tracks from top dynamical and consensus hurricane models as of 2:00 AM Monday 11th October 2021. (NCAR)

This tropical disturbance is riding along an expansive low to a mid-level high-pressure ridge to the northeast, gradually pulling eastward. The high-pressure system will result in Invest 93L moving west-northwest through the next five days, taking it across and north of Barbados and the French Antilles by Tuesday night.

As the ridge pulls eastward, Invest 93L will near the Leeward Islands and the Greater Antilles by Wednesday into Thursday as it moves northward in the Caribbean Sea.

Looking at the top global models, none of the EMCWF, GFS, or UKMET develop Invest 93L into an organized tropical cyclone over the next five days.

European (ECENS) latest ensemble model runs showing few ensemble runs developing this disturbance into an organized low-pressure system.
European (ECENS) latest ensemble model shows few ensemble runs developing this disturbance into an organized low-pressure system.

How Strong Can Invest 93L Get?

The takeaway: No operational, top models develop this system into an organized tropical cyclone over the next 5 days, with none reaching tropical storm strength.

Invest 93L's forecast intensity guidance from top dynamical, statistical, and consensus hurricane models as of 82:00 AM Monday 11th October 2021. (NCAR)
Invest 93L’s forecast intensity guidance from top dynamical, statistical, and consensus hurricane models as of 82:00 AM Monday 11th October 2021. (NCAR)

No top global models nor dynamical, statistical, and consensus hurricane models bring Invest 93L to a tropical storm strength.

As mentioned earlier, environmental conditions will be somewhat favorable for development over the next day or so. Still, strong upper-level winds and wind shear will limit intensification and consolidation of convection around a low-level circulation.

Based on the current forecast, the cyclone is forecast to move over warm sea surface temperatures between 28°C and 30°C in an environment with marginally high moisture. This atmospheric setup will still allow for pulses of convection to develop as the tropical wave moves westward over the next one to three days.

What impacts can we expect to see from Invest 93L?

For the entire island chain, regardless of development, scattered showers and thunderstorms are forecast to begin affecting the region from Monday evening and continue across the Lesser Antilles through Wednesday. Locally heavy rainfall and gusty winds in excess of 55 KM/H are likely, mainly north of T&T.

Total accumulated rainfall over the next 5 days from the GFS, EMCWF, and ICON models across the Lesser Antilles (Windy.com)
Total accumulated rainfall over the next 5 days from the GFS, EMCWF, and ICON models across the Lesser Antilles (Windy.com)

Invest 93L is forecast to move across the Lesser Antilles over the next 2-3 days, bringing scattered showers and thunderstorms mainly north of Trinidad and Tobago. Across the region, a high-moisture atmosphere will remain, providing fuel for shower and thunderstorm development. Wind shear is also forecast to diminish across the Windward Islands as the week progresses, allowing for longer-lived showers and thunderstorms across the region.

Scattered showers and thunderstorms, accompanied by gusty winds, are possible across Barbados, Trinidad, and Tobago from Monday evening through Tuesday. Similar conditions are forecast to spread northward across the remainder of the central and northern Lesser Antilles and Leewards by Tuesday night through Wednesday.

For Trinidad and Tobago, scattered showers and isolated thunderstorms are forecast mainly after midnight into Tuesday, with heavier rainfall and gusty winds remaining northeast of the country. Winds on Tuesday across T&T are forecast to be from the southeast to the south. This wind profile will result in showers and thunderstorms moving from the south to the north, possibly intensifying over the Gulf of Paria and the Northern Range and producing hazardous seas as well as street/flash flooding along the East-West Corridor.

Additionally, on Wednesday, surface to mid-level moisture trailing behind Invest 93L/Tropical Wave 55 will continue to stream across T&T and the Windwards. This atmospheric setup will allow for cloudiness, showers, and thunderstorms to persist across the region through the week.

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.

What should I do?

This system is not forecast to affect Trinidad and Tobago directly. Don’t panic. No direct tropical storm threats are heading to T&T, so feel free to ignore the “storm coming” chain messages that pass through WhatsApp every hurricane season.

If you are a risk-averse person, now is a good time to check your inclement weather, flood, or hurricane season plan, ensuring your preparedness supplies are not expired, stocked, and in a safe location.

The Office of Disaster Preparedness and Management has compiled a comprehensive guide for preparing for the Wet and Hurricane Season.

Tropical Cyclone Climatology

2021 has already produced 21 named tropical cyclones in the Atlantic Basin, with the following system being named Wanda for the 2021 Atlantic Hurricane Season.

As we head through October, we’ll continue to monitor the entire Atlantic closely as tropical cyclones could form from tropical waves, non-tropical low-pressure systems in the North Atlantic, and the Central America Gyre in the Western Caribbean Sea or the southwestern Gulf of Mexico.

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