Editor's note: This is a developing story and may be updated.

Hurricane Ian strengthened to a Category 4 storm early Wednesday (Sept. 28) morning having just passed over western Cuba, causing an island-wide blackout and killing at least two people. The storm's center is due to reach Florida's western shore within hours, the National Hurricane Center (NHC) warned at 11 a.m. ET on Wednesday.

Ian made landfall in Cuba on Tuesday (Sept. 27) as a Category 3 hurricane with maximum sustained winds around 125 mph (205 km/h). The cyclone was expected to dump some 6 to 10 inches (15.2 to 25.4 cm) of rain on the western half of the island, with some areas getting up to 16 inches (40.6 cm) of rainfall. State media reported two deaths in the western province of Pinar del Río, which endured heavy flooding and widespread destruction as the storm came ashore, CNN reported.

Cuba's entire power grid collapsed in the wake of the hurricane, and the western section of the three-part grid suffered the most damage, The New York Times reported. Some electricity had been restored on the eastern half of the island by Wednesday morning, but overall, it was unclear how much of the island still remained without power at that time.

As the storm swept into the southeastern Gulf of Mexico, it strengthened into a Category 4 storm with maximum sustained winds near 140 mph (220 km/h), the NHC reported at 5 a.m. ET. Two hours later, the storm intensified and began producing maximum sustained winds around 155 mph (250 km/h) — nearly reaching the Category 5 threshold of 157 mph (252 km/h).

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"Maximum sustained winds remain near 155 mph (250 km/h) with higher gusts," the NHC reported at 11 a.m. ET. "Ian is forecast to make landfall on the west coast of Florida as a catastrophic hurricane."

"Catastrophic storm surge inundation of 12 to 18 feet [3.6 to 5.5 meters] above ground level along with destructive waves are expected somewhere along the southwest Florida coastline from Englewood to Bonita Beach, including Charlotte Harbor," the NHC warned at 11 a.m. ET. "Catastrophic wind damage is beginning along the southwestern coast of Florida today near the landfall location. Hurricane-force winds are expected to extend well inland along [sic] near the core of Ian."

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Heavy rainfall is expected across the entire Florida peninsula through Thursday (Sept. 29). "Considerable" flooding is expected in southern and northern regions of the state, and portions of central Florida are forecasted to endure "widespread, life-threatening catastrophic" flooding, due in part to anticipated river flooding in the region, the NHC stated.

Originally published on Live Science.