Basic wind speed grades from roughly 170 mph in the Upper Keys near Key Largo up to about 180 mph at Key West. Open-water Exposure D makes the demand even harsher.
Monroe County runs from mainland Florida out through 113 miles of low islands to Key West. No point in the archipelago sits more than a few feet above mean sea level.
That geography drives the number. The islands face an open-water hurricane fetch in nearly every direction, so most sites are Exposure D under ASCE 7-22 Section 26.7.
Per ASCE 7-22 Figure 26.5-1B, the Upper Keys (Key Largo, Tavernier, Plantation Key) run about 170-172 mph for Risk Category II. The Middle Keys (Marathon, Duck Key, Long Key) land near 175 mph.
The Lower Keys (Big Pine, Sugarloaf, Cudjoe, Key West) hit roughly 180 mph — the highest contour on the entire map for standard occupancy, anywhere in the lower 48 states.
Verify the exact value for your address with the calculator. It reports the ASCE 7-22 contour the ZIP centroid lands in, then applies the correct Risk Category importance factor.
Pre-filled to Key West (33040). Edit the ZIP or risk category and the result updates live, citing whether the value comes from an FBC override or the ASCE 7-22 map.
The contour gradient from north to south is gradual but consistent. Values are ASCE 7-22 Figure 26.5-1B readings for Risk Category II.
| City / Island | Primary ZIP | Wind Speed (Cat II) | Position in Keys | Reference |
|---|---|---|---|---|
| Key West | 33040 | ~180 mph | Lower Keys terminus | ASCE 7-22 Fig 26.5-1B |
| Big Pine Key | 33043 | ~178 mph | Lower Keys | ASCE 7-22 Fig 26.5-1B |
| Marathon | 33050 | ~175 mph | Middle Keys | ASCE 7-22 Fig 26.5-1B |
| Islamorada | 33036 | ~172 mph | Upper Keys | ASCE 7-22 Fig 26.5-1B |
| Key Largo | 33037 | ~170 mph | Upper Keys / mainland approach | ASCE 7-22 Fig 26.5-1B |
The 1935 Labor Day Hurricane is the strongest US landfall ever recorded by barometric pressure: 892 mb at Craig Key on September 2, 1935, with sustained winds estimated near 185 mph.
It crossed the Middle Keys as a compact Category 5 and destroyed nearly everything between Tavernier and Marathon, including the Florida East Coast Railway extension to Key West. Over 400 deaths were confirmed.
Hurricane Irma made landfall at Cudjoe Key on September 10, 2017 as a Category 4 — maximum sustained winds 130 mph and central pressure 931 mb. Eyewall gust estimates reached 150 mph.
Older single-wides and pre-1992 stick-built homes were devastated. Structures built or renovated under the modern Monroe County code generally kept envelope integrity through the eyewall.
The Keys also absorbed Donna (1960), Betsy (1965), Georges (1998), and Wilma (2005). That landfall density — the highest of any US county for major hurricanes — is what the ASCE map reflects.
Permits in Monroe County are issued by the county building department plus the cities of Key West, Marathon, Islamorada, Key Colony Beach, and Layton. All adopt the Florida Building Code 8th Edition (2023) with ASCE 7-22 for wind loads.
Despite the highest ASCE wind speeds in the contiguous US, Monroe County is not part of HVHZ. Florida Building Code Section 1620 limits HVHZ to Miami-Dade and Broward counties only.
This surprises many designers. Keys projects use standard Florida Product Approval (FL#) listings rather than Miami-Dade NOAs, and TAS 201/202/203 testing is not jurisdictionally mandated.
Many coastal openings and roofing assemblies sold for Keys installation still carry that testing voluntarily, because the design pressures on Exposure D at ~180 mph are so high.
The single-road-out reality shapes Keys construction more than any provision. US 1 is the only land route off the chain, so mandatory evacuations begin 72+ hours before landfall — buildings must survive a major hurricane unoccupied.
Basic wind speed: ASCE 7-22 Fig 26.5-1B (~170-180 mph Risk Cat II, by Keys position).
Exposure: Typically D (open water) under ASCE 7-22 §26.7.
HVHZ status: Not HVHZ. Standard FL Product Approval applies.
Code edition: Florida Building Code 8th Edition (2023), ASCE 7-22 by reference.
Permitting authorities: Monroe County, Key West, Marathon, Islamorada, Key Colony Beach, Layton.
PE sign-and-seal: available nationwide through our P.E. network for permit-ready Engineering Reports.
The ASCE 7-22 Figure 26.5-1B map value for Key West is approximately 180 mph for Risk Category II, the highest design wind speed in the contiguous United States.
Verify the exact value for your ZIP with the calculator, which reports the contour the ZIP centroid lands in.
At the Cudjoe Key landfall on September 10, 2017, Irma was a Category 4 with maximum sustained winds estimated at 130 mph and a minimum pressure of 931 mb.
Eyewall gust estimates reached 150 mph.
The ASCE 7-22 map value there is around 180 mph for Risk Cat II, so Irma's sustained winds stayed under the code basic wind speed — yet older roofing and openings failed widely.
Most Keys structures face open water with no upwind obstructions, so ASCE 7-22 Section 26.7 typically puts them in Exposure D — the harshest category.
Exposure D raises the velocity pressure coefficient Kz versus B or C, increasing design pressures even before the high basic wind speed is applied.
No, and this is a common misconception. Florida Building Code Section 1620 defines HVHZ as Miami-Dade and Broward counties only.
Monroe County, despite the highest design wind speeds in the state, is not HVHZ.
Keys projects use standard Florida Product Approval rather than Miami-Dade NOA, and TAS 201/202/203 testing is not jurisdictionally required.
The ASCE 7-22 Figure 26.5-1B map shows a clear north-south gradient. Key West (Lower Keys) sits in the highest contour at roughly 180 mph Risk Cat II.
Marathon and the Middle Keys land near 175 mph. Key Largo and the Upper Keys taper toward 170-172 mph toward the south Miami-Dade coast.
Verify the exact value for your ZIP using the calculator.
Run a full ASCE 7-22 analysis for any Monroe County address — design wind speed, Exposure D pressures, and a permit-ready Engineering Report. Need it stamped? PE sign-and-seal is available in all 50 states.