Invest 90L – No Direct Threat to the Lesser Antilles

Since 8:00 AM AST Saturday, the National Hurricane Center has been monitoring a trough, in which an area of low-pressure developed and is now designated Invest 90L, for tropical cyclone development. This system is not forecast to impact the Lesser Antilles as it moves towards the northwest.

From the National Hurricane Center’s Tropical Weather Outlook, as of 8:00 AM, for Invest 90L, “A broad area of low pressure located about 350 miles east-northeast of the northern Leeward Islands is producing disorganized showers and thunderstorms with winds of around 30 mph on its northeast side. Some gradual development of this system is expected, and a tropical or subtropical depression could form during the next couple of days while it moves northwestward and then northward over the open Atlantic. After that time, upper-level winds are expected to become less conducive and the disturbance is forecast to merge with a frontal system after midweek, so additional development is not expected.

What We Know

Invest 90L is producing scattered showers and thunderstorms, mainly east of the low pressure. It has medium chances of development over the next 5 days. Credit: Weathernerds
Invest 90L is producing scattered showers and thunderstorms, mainly east of the low pressure. It has medium chances of development over the next 5 days. Credit: Weathernerds

A broad 1008 millibar low-pressure area near 19N56W is producing disorganized scattered moderate convection from 14N-20N between 48W-55W. Strong winds near 46 KM/H (25 knots) extend outward several hundred nautical miles in the NE quadrant of the low.

A tropical or subtropical depression could form during the next couple of days while it moves northwestward and then northward over the open Atlantic. The disturbance is forecast to merge with a frontal system after midweek and further development is not expected by that time.

As of the 8:00 AM Tropical Weather Outlook, this system has a medium chance, 50%, of tropical cyclone formation over the next 48 hours and a medium chance, 50%, of tropical cyclone formation over the next 5 days.

The system is located in an area of marginally favorable upper-level divergence and low-level convergence. It also had a good deal of vorticity but strong westerly wind shear has kept showers and thunderstorms to the east of the low-pressure system. A large area of dry air remains northeast of the low-pressure.

Conditions appeared favorable marginal for development, with the SHIPS model diagnosing moderate wind of shear 15–25 knots through the next 60 hours, becoming strong later this week, in excess of 30 knots. The SHIPS model also forecasts warm SSTs near 28°C and a fairly supportive moisture envelope through the next 2-3 days.

What We Forecast For Invest 90L

Track

Invest 90L's path and potential area for development northeast of the Leeward Islands. Credit: National Hurricane Center
Invest 90L’s path and potential area for development northeast of the Leeward Islands. Credit: National Hurricane Center

Invest 90L is forecast to move mostly northwestward over the next 2-3 days, well northeast of the Leeward Islands. With strong westerly wind shear, much of the showers and thunderstorms are forecast to remain east of the low-pressure system.

After day three, this low-pressure system is forecast to merge with a cold front and then moves towards the northeast, becoming post-tropical.

 The EMCWF (EPS/ECMF) ensemble models for Invest 90L as of 00Z Monday 18th November 2019. Credit: Alan Brammer
The EMCWF (EPS/ECMF) ensemble models for Invest 90L as of 00Z Monday 18th November 2019. Credit: Alan Brammer

There is great consistency in the forecast track of this system. Based on model guidance. The EMCWF (European), GFS (US) and UKMET (UK) all bring this system northwest through 48-72 hours, then a turn towards the northeast, into the North-Central Atlantic. Other top models, like the ICON (German) and ARPEGE (French), have similar outputs to the EMCWF and UKMET.

Intensity

Most models keep this system as a weak tropical storm as it moves towards the northwest and then northeast. The next name on the list of names for the 2019 Atlantic Hurricane Season is Sebastien.

Nearly all models (EMCWF (European), GFS (US), UKMET (UK), ICON (German), ARPEGE (French) and CMC (Canadian)) keep the gustiest winds and heavy rainfall east of the Leeward Islands, though a weak wind regime and deep tropical moisture may support localized afternoon showers and thunderstorms.

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.

Always check the National Hurricane Center for the latest information for tropical cyclones and your local meteorological offices for country-specific advisories concerning Invest 90L.

What is an Invest?

It sounds ominous, but from the outset, it really isn’t. Invest is short for investigation, followed by the numbers 90 through 99 and either the letter “L” for the Atlantic basin systems or “E” for the Eastern Pacific Systems.

This naming convention is used by the National Hurricane Center to identify features they are monitoring for potential future development into a tropical depression or a tropical storm.

According to the National Hurricane Center, by designating a tropical weather system as an “Invest”, the collection of specialized data sets and computer model guidance on the area of interest can begin. This collection and processing of data are shown on a number of government and academic websites for analyzing.

That said, the “Invest” assignment does not correspond to how likely a system may develop into a tropical depression or storm.

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