An invest is an area of disturbed weather that a forecasting centre has singled out for closer study. Giving it an identifier lets different teams file satellite images, observations and model runs under one name and follow the same disturbance over time.
Meteorix illustration of the weather pattern.
In the Atlantic and eastern Pacific, forecasters use the numbers 90 through 99 for invests. The letter L identifies the Atlantic basin, which includes the Caribbean Sea and the Gulf of Mexico. E identifies the eastern Pacific. That’s how 92L and 92E can appear on the same day.
The numbers are reused, so if you save a satellite image, keep the date alongside the code. The 92 in 92L tells you nothing about wind speed, hurricane category or the percentage chance of formation.
Suppose the US National Hurricane Center (NHC) gives a disturbance a 60% chance of formation within seven days. That figure answers a specific question. How likely is a tropical or subtropical cyclone to form during that period? Check the time window when reading the outlook. The probability for the first 48 hours can be different.
For someone in Puerto Rico, Veracruz or Havana, the more immediate question is “What weather will we get here?” The formation probability alone cannot tell you the odds of local impacts. A system might develop far offshore and move away, or bring heavy rain to land while it is still poorly organised.
Imagine that the most persistent thunderstorms today sit east of a broad low. One model develops a small circulation centre underneath those storms. Another places the centre farther west. The tracks already have different starting points before you follow either line forward. While the centre is poorly defined, tracing one line to a particular town suggests more precision than the observations allow.
When comparing cyclone tracks, check when each model run began. Do the models place the initial centre in roughly the same area? How far ahead do their tracks begin to diverge? For the official formation probability and its time window, consult the NHC outlook.
Open the Meteorix map ↗The number identifies the disturbance. The NHC publishes the probability of formation separately in its tropical weather outlook.
For official forecasts and warnings, consult your national weather service.
The axis of a tropical wave can cross an island in the morning and the downpours arrive hours later. To understand the timing, follow both the wind and the clouds.
A wind circulation can stretch across several countries between the Caribbean and the Pacific. To see which places bear the brunt of the rain, look for the river basins that one rainband after another passes over.
When a low-pressure system deepens unusually quickly, meteorologists call it explosive cyclogenesis. Learn what they measure, why latitude matters and how to track it on a pressure map.
Cloud height and shape can help you interpret a changing sky. Learn to recognise the main cloud layers and read the Meteorix cloud cover map.
Some cut-off lows pass almost unnoticed. Others help produce extraordinary rainfall. The difference depends partly on what happens below them.