Sierra Madre terrain appeared to temper Hurricane Simon as its eye passed 50 km off Mexico
Hurricane Simon passed about 50 km off Mexico's Pacific coast on Oct. 11 as a Category 4 storm with winds near 210 km/h, NASA reported. The Sierra Madre appeared to shrink its wind field, while news reports described flooding in Manzanillo.
The Scientist · Science desk
Key figures for Hurricane Simon: sustained winds reached 250 km/h as it crept north-northwest; sustained winds were about 210 km/h at the time of the Suomi NPP image; it passed close to the Mexican coast as a Category 4 storm.
| Figure | Value | Note | Claim |
|---|---|---|---|
| Sustained winds reached as Simon crept north-northwest | 250 km/h | 2 | |
| Winds at Suomi NPP image | 210 km/h, about | 1 | |
| Category near the coast | 4 category | 3 |
What happened
- Suomi NPP's VIIRS imaged the storm around 2:30 p.m. local time on Oct. 11, with the eye between Manzanillo and Puerto Vallarta.
- A nighttime NOAA-21 VIIRS image from the early hours of Oct. 11 shows atmospheric gravity waves radiating from the hurricane.
- On the morning of Oct. 13, forecasts of Simon's intensity and path were still rated "very low confidence" as the storm kept defying meteorologists' expectations.
Why it matters
- What it limits constraint A track that may swing north into the Gulf of California before landfall leaves operators along the coast without a fixed landfall point to plan around.
- Who's exposed exposure Large swells making nearshore conditions dangerous were expected on the southwestern and west-central coasts in the coming days, so shipping and coastal work there faces a sea hazard that outlasts the Oct. 11 pass.
- What's now possible capability Airglow ripples let a satellite see a hurricane's effect near the mesosphere, but only on nights when the Moon is dim enough that reflected light does not wash them out.
NASA's account carries two sustained-wind figures for Simon, 250 km/h and 210 km/h, a gap of 40 km/h or 16% [17]. The National Hurricane Center supplied the 210 km/h figure for the time of the Suomi NPP image [1]. The 250 km/h figure is a speed the storm reached as it crept north-northwest [2], and the account does not say when. We would use 210 km/h for the Oct. 11 pass and would not assign the 40 km/h to terrain.
The terrain finding is narrower than the gap. NASA wrote that the NHC noted the Sierra Madre's topography "appeared to temper the storm's intensity somewhat and shrink the size of its wind field" [7]. The wording is hedged twice, with "appeared" and "somewhat". NASA also described the inner core as brushing up against the coast at the time of the image [6].
A smaller wind field and a flooded port are compatible, and NASA reports both. The heavy rain and flooding in Manzanillo, and the raised mudslide risk in mountainous areas, rest on news reports [8]. NASA's reference list includes a Reuters article of Oct. 12 headlined "Hurricane Simon crawls along Mexico's Pacific coast, bringing floods and evacuations" [9].
The gravity waves are a separate observation, and a conditional one. Latent heat released near the eyewall drives strong convection and tall cumulonimbus clouds, and their updrafts can send waves into the stratosphere and mesosphere [11]. Winds in the upper atmosphere can dissipate the waves before they reach the mesosphere, where they show up as ripples in airglow [12]. The NOAA-21 image from the early hours of Oct. 11 [10] therefore shows that waves reached that height on one night. The thing it doesn't tell you is how often Simon's waves do, since the same source says they are not always observable [12].
What to watch
- Whether Simon enters the Gulf of California before landfall, as NASA said it might.
- Whether later NHC advisories lift forecast confidence above "very low".
- Whether official damage counts confirm the flooding and mudslide reports around Manzanillo, which so far rest on news accounts.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence68
- Adoption
- Not scored
- Hype gap−5
- Incentives
- Not scored
- Confidence62
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
At the time of the Suomi NPP image, sustained winds were about 210 kilometers (130 miles) per hour, according to the National Hurricane Center.
- [2]
Sustained winds reached 250 kilometers (155 miles) per hour as Simon crept north-northwest.
- [3]
Hurricane Simon passed close to the Mexican coast as a category 4 storm on October 11, 2026.
- [4]
Simon's eye was about 50 kilometers (30 miles) offshore on October 11.
- [5]
When VIIRS on the Suomi NPP satellite acquired its image around 2:30 p.m. local time (20:30 UT) on October 11, the eye was between Manzanillo and Puerto Vallarta.
- [6]
At the time of the image, the storm's inner core was brushing up against the coast.
- [7]
The topography of the Sierra Madre mountains appeared to temper the storm's intensity somewhat and shrink the size of its wind field, the NHC noted.
- [8]
The major hurricane delivered heavy rain and flooding to coastal areas, including the port city of Manzanillo, and raised the risk of mudslides in mountainous areas, according to news reports.
- [9]
NASA's reference list includes a Reuters article dated October 12, 2026, titled "Hurricane Simon crawls along Mexico's Pacific coast, bringing floods and evacuations."
- [10]
A nighttime VIIRS image from the NOAA-21 satellite, acquired in the early morning hours of October 11, shows atmospheric gravity waves radiating from the hurricane.
- [11]
Gravity waves form when latent heat released near the tropical cyclone's eyewall drives strong convection, building tall cumulonimbus clouds with updrafts that can send waves into the stratosphere and mesosphere.
- [12]
The waves are not always observable: winds in the upper atmosphere can dissipate them before they reach the mesosphere, where they show up as ripples in airglow, faint light emitted by gases at those altitudes.
- [13]
The VIIRS day-night band is sensitive to airglow but also detects reflected moonlight, which can wash it out; on the night of the image, minimal illumination from the Moon helped the airglow stand out.
- [14]
On the morning of October 13, forecasts of Simon's intensity and path remained "very low confidence," as the storm's evolution continued to defy meteorologists' expectations.
- [15]
The system may steer north and enter the Gulf of California before making landfall.
- [16]
Large swells causing dangerous nearshore conditions were expected along portions of the southwestern and west-central coasts of Mexico in the coming days.
- [17]
The two sustained-wind figures differ by 40 km/h, a drop of 16% from 250 km/h to 210 km/h.
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Sources
1 independent publisher whose own reporting we read for this story.
- nasa.govHurricane Simon Lurks Off the Mexican Coast
1 article · October 13, 2026
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Topics
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Entities
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