This blog post explains the latest update from the National Hurricane Center regarding Invest 91L, a tropical disturbance in the Atlantic that had briefly attracted interest for possible development.
I summarize what forecasters reported, why the system weakened, and where the NHC’s attention is shifting next.
As someone with three decades of experience in tropical meteorology, I will also provide context on why many promising invests fail to develop and what indicators to watch going forward.
What the National Hurricane Center reported about Invest 91L
The NHC has continued to reduce the chances that Invest 91L will become a tropical depression or tropical storm.
Over the course of the week the disturbance steadily lost organization, and on Saturday morning forecasters again downgraded the probability of development.
The system’s decline reflects both a clear weakening trend and the reality that environmental conditions are not supportive of significant tropical growth at this time.
Why the disturbance weakened and what that means
When an invest that initially shows potential begins to lose structure, it usually reflects one or more hostile environmental factors.
In this case the NHC cited a loss of organization; while they did not single out a single cause, several common mechanisms likely contributed.
From my experience, the factors that commonly inhibit tropical development include vertical wind shear that tears convection apart, intrusions of dry air that choke thunderstorms, and unfavorable sea surface temperatures or ocean heat content.
Any of these can disrupt the core convection necessary for a closed low to form and strengthen.
Key reasons disturbed systems like 91L fail to develop:
Forecasting challenges highlighted by the decline
The weakening of Invest 91L underscores how challenging tropical forecasting remains.
Even with modern satellites, scatterometer data, and high-resolution models, small changes in the atmospheric environment can rapidly alter a system’s prospects.
Predicting genesis requires accurate representation of small-scale convective processes and larger-scale environmental conditions — both of which continue to present forecasting uncertainty.
What the NHC is doing now and what to watch next
With 91L trending downward, the NHC is shifting focus to other potential areas of concern across the basin.
This is standard practice: resources and forecast attention are concentrated where the probability of development is higher.
For residents, mariners, and emergency managers, the important takeaways are vigilance and context.
A single invest’s failure to develop does not reduce the overall hurricane season risk — it simply refines where and when threats may emerge.
Practical things to watch in the coming days:
Here is the source article for this story: Atlantic tropical activity stifled as Invest 91L odds drop even further | Latest Weather Clips