A tropical wave, which INSIVUMEH calls an onda del este (easterly wave), is a disturbance that travels across Guatemala from east to west with the trade winds during the rainy season, bringing rain that can be heavy and accompanied by lightning. In a historical September notice, INSIVUMEH reported 41 easterly waves over the country that year. This page explains what they are, how they differ from hurricanes and what the institute reported about the waves of 2026.
Quick summary: What it is: a cloud system that moves off the African coast and is carried westward by the trade winds, producing rain as it passes (INSIVUMEH). Vertical extent: the institute’s study describes most tropical wave disturbances generally as shallow, 0 to 8 km in height. Historical 2026 counts: 39 in one September notice, including five during September, and 41 in another. Different from a hurricane: some waves acquire vorticity and develop into tropical cyclones; the study says only a few disturbances do so. Risks: rising rivers, flooding, landslides and lahars. Emergencies: 119.
What an easterly wave is, according to INSIVUMEH
INSIVUMEH describes the rainy cycle this way: as the northeast trade winds become established and the intertropical convergence zone approaches these latitudes, cloud systems move off the African coast. The trade winds carry them westward with a stronger easterly component. These are easterly waves. They generate rain as they pass, and sometimes acquire a vorticity component that turns them into tropical cyclones.
In its study Variabilidad y Cambio Climático en Guatemala (Climate Variability and Change in Guatemala), from February 2018, the institute explains that several types of wave disturbances occur in the tropics. Only a few develop into cyclones. Most are shallow atmospheric disturbances, 0 to 8 km in height, traveling from east to west within the trade winds. That depth description concerns tropical disturbances in general, not only tropical waves. The same study also uses the terms easterly wave and tropical disturbance together.
The easterly waves of 2026, date by date
These are historical notices and forecasts. A forecast of a wave’s arrival does not establish that it passed on the predicted dates.
| Notice context | What INSIVUMEH said |
|---|---|
| July 6 notice | Easterly wave No. 16 of the season was expected that Monday night and during Tuesday; the largest rainfall totals were forecast for the Franja Transversal del Norte, the Caribbean region, Bocacosta, Petén and the southern Central Highlands |
| Forecast for July 14 and 15 | Wave No. 19 was expected to enter between Tuesday, July 14, and Wednesday, July 15; moderate to heavy rain was forecast for Bocacosta, the Franja Transversal del Norte and the Caribbean region |
| Alta Verapaz rainfall notice | Rain was attributed to incoming moisture and easterly waves from the Caribbean Sea; six municipalities had soil saturation equal to or greater than 90% in the upper layer |
| September notice reporting 39 waves | 39 waves counted that season, five during September. The institute said the rain discussed in that notice was not associated with easterly waves or tropical cyclones |
| September notice reporting 41 waves | 41 waves recorded over Guatemala that year; more were expected during September. At the time of the notice, no tropical cyclone was forecast to approach or develop in a way that would directly affect the country’s weather |
| Forecast for September 26 and 27 | Rain was forecast because of low-pressure areas south of Mexico and the possible approach and passage of an easterly wave |
The notices report wave numbers and seasonal counts, rather than a dated list of every wave.
Easterly wave, depression, storm or hurricane
| System | What it is | Where to follow it |
|---|---|---|
| Easterly wave (tropical wave) | A disturbance carried from east to west by the trade winds that brings rain as it passes (INSIVUMEH) | INSIVUMEH’s daily forecast and notices |
| Tropical cyclone (depression, storm or hurricane) | A system that can form when a disturbance acquires a vorticity component; INSIVUMEH explains that some easterly waves develop into cyclones, while its study says only a few tropical wave disturbances do so | Storm and hurricane tracker |
| Rain without a wave | INSIVUMEH also attributes rain to low-pressure systems, moisture from both coasts or the monsoon trough. In its September notice reporting 39 waves, it said the rain discussed there was normal for the season and was not caused by waves or cyclones | CONRED weather alerts |
INSIVUMEH’s notices identify seasonal wave numbers, including No. 16 and No. 19, and announce which regions are expected to receive the largest rainfall totals.
What to do when a wave is announced
When INSIVUMEH announced wave No. 19, it warned that the rain could cause:
- sudden rises in rivers and streams;
- flooding in vulnerable areas;
- landslides on hillsides;
- lahars descending along the volcanic chain during heavy rainfall.
Its advice is to stay informed through official bulletins and forecasts. In its notice for September 26 and 27, it also advised avoiding swollen rivers and areas susceptible to flooding, and following local authorities’ recommendations. Check CONRED weather alerts for alerts; for emergencies, call 119, the national emergency number identified by CONRED.
Where to read the daily notice: INSIVUMEH publishes its daily forecast as a PDF and posts notices on its website. Check the date inside the PDF before using it for travel decisions.
How waves fit into the rainy season
According to INSIVUMEH, the rainy season runs from May through October. It generally begins in May; June brings cloudy, rainy days; July and part of August bring the dry spell called the canícula; and September and October bring the return of heavy rain that completes the season.
Easterly waves are one source of that rain, alongside the intertropical convergence zone. In a September 2017 case, INSIVUMEH attributed extreme rain in Bocacosta to an easterly wave combined with the approaching intertropical convergence zone. It noted that the convergence zone normally lies near Guatemala in September and that easterly waves pass during the rainy season.
For regional rainfall information, see Guatemala’s climate zones. For this year’s season, read the 2026 rainy-season guide and the 2026 canícula guide.
Related
- Storms and hurricanes near Guatemala today
- CONRED weather alerts today
- Guatemala’s climate zones
- Where to live in Guatemala by climate
Sources
- INSIVUMEH: July notice forecasting wave No. 16, forecast for wave No. 19, and Alta Verapaz rainfall notice.
- INSIVUMEH: historical September notices reporting 39 waves and 41 waves, and the forecast for September 26 and 27.
- INSIVUMEH, Variabilidad y Cambio Climático en Guatemala, Departamento de Investigación y Servicios Climáticos, February 2018. The study supports the descriptions of tropical disturbances, the seasonal cycle and the September 2017 rainfall example.
Frequently Asked Questions
What is a tropical wave or easterly wave?
It is a weather disturbance that travels from east to west with the trade winds. INSIVUMEH explains that, when the northeast trade winds become established and the intertropical convergence zone approaches these latitudes, cloud systems move off the African coast and the trade winds carry them westward. These easterly waves generate rain as they pass. Its 2018 study describes most tropical wave disturbances generally as shallow, extending from 0 to 8 km in height.
How many easterly waves have passed through Guatemala in 2026?
INSIVUMEH’s historical September notices reported 39 waves, five of them during September, and 41 waves in another notice. These are historical counts rather than a current season total. For September 26 and 27, 2026, the institute forecast the possible approach and passage of another easterly wave.
Is a tropical wave the same as a hurricane?
No. INSIVUMEH explains that some easterly waves acquire a vorticity component and become tropical cyclones. Its study says only a few tropical wave disturbances develop into cyclones; easterly waves also bring rain without becoming cyclones. Use our hurricane tracker to check for an active cyclone near Guatemala.
Which regions of Guatemala receive the most rain from an easterly wave?
It depends on the wave. For wave No. 16, forecast for the night of July 6 and the following Tuesday, INSIVUMEH expected the largest rainfall totals in the Franja Transversal del Norte, the Caribbean region, Bocacosta, Petén and the southern Central Highlands. For No. 19, forecast for July 14 and 15, it highlighted Bocacosta, the Franja Transversal del Norte and the Caribbean region.
When do easterly waves pass through Guatemala?
During the rainy season, which INSIVUMEH describes as May through October. The institute uses seasonal wave numbers: it forecast No. 16 for the night of July 6 and the following Tuesday, and No. 19 for July 14 and 15. A historical September notice reported 39 waves that season. These forecasts do not by themselves confirm that a wave passed on those dates.
What risks does an easterly wave bring?
INSIVUMEH’s notices warn of sudden rises in rivers and streams, flooding in vulnerable areas, landslides on hillsides and lahars along the volcanic chain during heavy rain. For emergencies, call 119, the national emergency number identified by CONRED.
