Miami Lowest Temp May 21: What the Market Says

Miami in late May runs on a predictable thermodynamic script. Sea surface temperatures in Biscayne Bay sit in the low 80s. The Atlantic high-pressure ridge parks warm, humid air over South Florida. Overnight lows rarely dip below 75°F once the calendar flips past mid-May. That’s the climatological baseline. The market is now pricing one specific outcome against that backdrop: a lowest temperature of 78 to 79°F on May 21, 2026, sitting at 28% probability.

The structure here is a multi-outcome market, not a binary YES/NO contract. Ten temperature bands compete, ranging from 73°F or below all the way to 92°F or higher. The 78 to 79°F band carries 28% probability. The 76 to 77°F band and the 80 to 81°F band absorb much of the remaining probability mass. With total volume at $1,336 and resolution set for 2026-05-21 at noon, this market is thin. Thin markets move sharply on new data, and a single overnight forecast update could reprice every band before Wednesday.

How the 78 to 79°F Contract Works

This contract pays out if Miami’s recorded lowest temperature on May 21, 2026, falls specifically in the 78 to 79°F range. The market resolves at 2026-05-21 12:00:00. Resolution follows the designated weather data source for the market, which tracks official Miami temperature readings, most likely from Miami International Airport (KMIA), the standard National Weather Service observing station for the city.

• 78-79°F band (primary outcome): $0.28 per contract, 28% implied probability.
• 76-77°F band: competing outcome pulling meaningful probability below the primary band.
• 80-81°F band: competing outcome pulling probability above the primary band.
• 73°F or below: extreme cold scenario, very low probability in late May Miami.
• 92°F or higher: extreme heat scenario for overnight low, essentially negligible.

The primary band misses when the overnight low lands outside 78 to 79°F entirely. National Weather Service data from KMIA shows Miami’s late-May overnight lows cluster between 75°F and 80°F historically. Any shift in the synoptic pattern, a front pushing through, an easterly wind surge off the Atlantic, or a stalled cloud deck, moves the actual low into adjacent bands. The 76 to 77°F and 80 to 81°F bands are the real competition here, not the extremes.

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Momentum and Market Signals

The momentum composite for this contract shows zero movement across both the 1-hour and 24-hour windows, with a trend score of 18.26. That flat signal reflects a market that has priced its best guess and is now waiting for updated forecast models, specifically the National Weather Service’s short-range output for South Florida, to give traders a reason to move capital between bands.

Total volume stands at $1,336, with all of that volume recorded in the past 24 hours. Liquidity sits at $10,489 in the order book. This is a low-volume market. That $10,489 in order book depth sounds meaningful, but with volume this thin, a single trader updating their position based on Tuesday evening’s forecast could shift the 78 to 79°F band’s price by several percentage points in minutes. The market is pricing uncertainty, not science, and the science on late-May Miami lows is actually fairly settled.

• 1h change (+0.0%) and 24h change (+0.0%): Zero movement signals market consensus has stabilized at 28%, pending new meteorological data.
• Trend score (18.26): Low trend activity consistent with a market in a holding pattern ahead of resolution.
• Volume ($1,336 total): Extremely thin. Any new NWS forecast or model run before May 21 could move prices sharply across all bands.
• Liquidity ($10,489): Provides some buffer, but not enough to absorb a major repositioning event without price impact.
• Open interest ($0): Suggests positions are either fully hedged or this reflects a data artifact in a very early-stage market.

Lines Analysis: Miami’s Thermodynamic Context

Here’s what the measurements are telling us. Miami’s climatological record for late-May overnight lows at KMIA shows a strong central tendency between 75°F and 79°F. The 78 to 79°F band capturing 28% is not unreasonable as a modal estimate. The adjacent 76 to 77°F and 80 to 81°F bands together likely absorb the majority of the remaining probability, which is consistent with how temperature distributions work around a mean: the tails get thin fast.

What makes the primary band lose is straightforward. A shift in the synoptic pattern before May 21 that pulls the overnight low either cooler (a weak front or increased easterly flow) or warmer (a strengthening ridge and high dewpoints) pushes the actual reading into a neighboring band. The data doesn’t care about the politics of which band traders have backed. May 21 falls on a Thursday, and the NWS 7-day forecast issued Tuesday or Wednesday morning will be the single most important data point before resolution. If that forecast shows overnight lows in the low 80s, capital will rotate into the 80 to 81°F band. If it shows 76 to 77°F, the lower band benefits.

• National Weather Service Miami forecast for May 20 to 21 overnight: the release of the Tuesday evening forecast package will be the primary repricing catalyst.
• GFS and European model ensemble agreement: strong model consensus on overnight low temperature narrows uncertainty and concentrates probability in one or two bands.
• Atlantic sea surface temperatures: elevated SSTs increase the likelihood of warmer overnight lows, supporting bands at 80°F and above.
• Cloud cover and precipitation: a cloud deck or overnight rain event on May 20 prevents radiative cooling, pushing the low toward 79 to 81°F. Clear skies allow more cooling, supporting 76 to 78°F.
• Subtropical high position: a strong, well-positioned Bermuda High locks in warm, humid overnight air across South Florida.

With volume at $1,336, this market has not attracted significant capital. The thin trading means the 28% price is a rough consensus, not a precise forecast. The NWS short-range forecast model output, available 48 to 72 hours before May 21, will functionally resolve the meteorological uncertainty before the market itself closes.

LINES VERDICT

Narrow Band, Thin Market

The 78 to 79°F band is a reasonable central estimate for a late-May Miami overnight low, but the market’s thin volume means this 28% price reflects limited trader conviction rather than deep meteorological analysis. The NWS forecast issued Tuesday will tell you far more than this order book.

What the market says: At 28%, traders are giving the 78 to 79°F band slightly better than one-in-four odds. That’s consistent with a multi-outcome market where probability is spread across adjacent bands. With resolution on May 21 at noon and volume under $2,000, this price can move sharply and quickly on a single forecast update.

Key unknown: The National Weather Service Miami overnight low forecast for May 20 to 21, expected in the Tuesday evening model package, is the single data point that will either confirm the 78 to 79°F band or push capital into the 76 to 77°F or 80 to 81°F alternatives.

Scientific Context: Miami’s Late-May Temperature Baseline

Miami’s climate in late May sits firmly in its hot, humid pre-hurricane season pattern. NOAA climate normals show average overnight lows at KMIA in late May ranging from 74°F to 78°F, with warmer-than-normal years pushing the average toward 79 to 80°F. Given the current period of elevated Atlantic sea surface temperatures and the persistent warm anomaly across South Florida in 2025 and 2026, overnight lows trending toward the upper end of the historical range are plausible. The 78 to 79°F band sits right at the intersection of the historical norm and the recent warm bias. The 80 to 81°F band captures the scenario where the warm anomaly persists into the overnight hours on May 21. Before resolution at 2026-05-21 12:00:00, any updated NOAA or NWS short-range forecast that pins the overnight low at 80°F or above would likely move capital out of the 78 to 79°F band and into its warmer neighbor.

Frequently Asked Questions

• What does 28% probability mean for this contract? The market assigns roughly a one-in-four chance that Miami’s lowest temperature on May 21 falls in the 78 to 79°F range. Other temperature bands absorb the remaining 72% of probability across nine alternative outcomes.
• What happens if the actual low is 77°F? A recorded low of 77°F resolves in the 76 to 77°F band, not this contract. The 78 to 79°F contract pays nothing. Adjacent band contracts capture that outcome instead.
• What data event would move this contract’s price most? The National Weather Service Miami short-range forecast for May 20 to 21 overnight, expected Tuesday evening, is the primary catalyst. Any significant deviation from the current forecast would reprice multiple bands simultaneously.
• When does this market resolve? Resolution is set for 2026-05-21 12:00:00, using official Miami temperature data, most likely from the KMIA National Weather Service station, to confirm the overnight low reading.
• Is the $10,489 in liquidity enough to trust this price? With only $1,336 in total volume, the 28% price reflects limited trading activity. The order book has depth, but thin volume markets can reprice sharply when a single informed trader updates a position based on new forecast data.