Day sail
Annapolis → St Michaels
26 nm · half-day
◆GO
Light westerly gradient off a 1015 mb ridge; benign seas throughout; all four legs manageable with mild motion.
Most weather apps tell you what's happening where you are. We model what's happening where you'll be.
Our Multi-Dimensional Dead-Reckoning Engine projects your boat's position hour by hour, then reads the forecast at each of those points. You get the conditions you'll actually feel underway, and one clear call for the passage — GO, CAUTION, MARGINAL, NO-GO, or DIVERT — with the reasoning in plain language.
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Every recommendation is grounded in the same models and marine forecasts a working navigator needs — coastal and offshore zone forecasts, active alerts, high-seas guidance. The models get blended with per-model weights tuned by forecast lead time, not pulled from a single source.
The organizations named above are identified solely to disclose the sources of the underlying data. They do not review, approve, or endorse WeatherWindow.AI or any analysis it produces, and no affiliation, sponsorship, or partnership is implied.
Every passage starts with the same homework — pulling the models, reconciling where they disagree, and turning tabs of raw output into a single go-or-no-go call. That's genuine meteorological work, usually under time pressure before a dawn departure, with your crew's comfort and safety on the line.
Type coordinates, tap your GPS, drop a pin, or import a GPX. Add waypoints to draw the route, then set your departure date and local time.
Hull type, dimensions, sail plan, fuel capacity. Upload polars if you have them. Every speed, ETA, motion rating, and fuel estimate is your boat's, not a generic hull's.
The Dead-Reckoning Engine calculates your position hour by hour and queries the conditions at each point. We synthesize it into a report that evaluates each leg, reads the surface weather charts, and calculates the apparent angles, so that you can project how your boat will experience the weather on your trip. Already at sea? Re-run from your current position.
Fuses live wind, waves, and current with your boat's polars, dimensions, and engine data to calculate where you'll actually be, then reads the forecast at that future position, hour by hour, as the apparent wind and waves your boat will feel. Every figure is calculated from the forecast and your boat's data.
Where every passage comes down to one plain-language recommendation. The engine's calculated conditions, the forecast models, and the surface charts are synthesized into a single report written for a mariner, not a meteorologist. Every wind and wave value is calculated by the engine and shown as apparent values; the AI narrates the forecast from our calculated numbers. You make the final decision.
Surface analysis charts from worldwide meteorological agencies, read with AI chart vision — pressure systems, fronts, and gradient winds. The source chart sits alongside the AI's reading, so the Captain can verify the interpretation directly.
7 wind and 4 wave models, weighted by forecast lead time, on a 16-day horizon. The report shows where the forecast is reliable and where model agreement is lower — so you know which decisions need a second look closer to departure.
Our Multi-Model Blend cross-checks the major weather models on every analysis. Ensemble Forecasts go even further: 200+ parallel forecast iterations across 5 model families, run along your boat's own dead-reckoned track. We draw them graphically as a spread, hour by hour, so you can see how much the forecasts agree or disagree. Watch them converge where they line up and fan out where they don't. A Captain's plan exclusive.
Monohull or catamaran, your polars, dimensions, and engine data drive every number: speed, ETA, heading, COG, motion comfort, and fuel. All wind and wave data shown as apparent — what your boat actually experiences.
An interactive Passage Map with a time scrubber. Tap any hour to see AWA, TWA, AWS, apparent wave angle, SOG, COG, heading, and a projected wind rose for that exact position in time.
GO / CAUTION / MARGINAL / NO-GO / DIVERT. Color-coded, with plain-language reasoning under every call that a mariner without a meteorology degree can read.
Squall and Lightning Indices scored 0–100 at every projected position, so convective risk is clearly listed instead of buried in the raw data. Convection is inherently hard to forecast — a low score is not an assurance that a squall will not develop. Included on the Skipper and Captain plans.
Anchorages and marinas within 100 nm, listed in case you get into trouble — so the Captain can independently verify a shelter's suitability before diverting to it.
Bring routes in from your nav software. Export back to your chartplotter. The route you planned is the route on your chart.
Your boat's track is calculated. The engine computes where you'll be, and the AI model then narrates the forecast in plain language. Cast off at 06:00 Saturday and you won't reach open water until Sunday morning. Your worst conditions may hit Tuesday afternoon, 280 nm from your current position. WeatherWindow projects your boat's hour-by-hour position, heading, COG, and importantly, the apparent wind and wave direction: the weather at your position, hour by hour.
Classic dead reckoning is two-dimensional: speed and time. Ours is multi-dimensional: it fuses live atmospheric, marine, and vessel data to project your position and heading hour by hour, then calculates the apparent conditions you'll actually experience at that hour. It feeds the current conditions, your boat's polars, dimensions, and engine data into our Multi-Dimensional Dead-Reckoning Engine, then queries live weather models at your future position, at that future time. That's how we catch the deterioration your trip briefing missed — not by being smarter than the models, but by asking them the right question.
What comes back is an analysis of your boat, on your passage, on your timeline.
Ensemble Forecasts show you how much the weather models agree or disagree. A single forecast is one prediction of the future, but an ensemble runs the weather multiple times (each iteration is called a member), each from slightly different starting conditions, to see the spread of possibilities. We ingest 200+ of these forecasts across 5 ensemble model families along your boat's own dead-reckoned track, and calculate the apparent wind and waves your boat will actually feel. Where the ensemble members cluster, the models agree. Where they fan apart, those days have more uncertainty, and you'll know exactly which days to re-check before you leave the dock or while you're underway.
Every recommendation comes with the headline, the reasoning, and the numbers that drove it. When wind model spread is elevated, you'll see a range — not a false single-number certainty.
Favorable gradient and manageable seas throughout. Moderate squall risk Day 4 only, well within vessel limits.
Squall and lightning are shown as 0–100 risk scores. Illustrative examples, actual reports vary in content and detail. WeatherWindow.AI is a decision-support tool, not a weather routing service. It does not replace official marine forecasts, a professional router, or your own judgment.
Whether it's an afternoon trip across the Chesapeake, a weekend up Puget Sound, or an Atlantic crossing, the analysis runs the same way on your boat's own track.
Light westerly gradient off a 1015 mb ridge; benign seas throughout; all four legs manageable with mild motion.
Light SW gradient with calm seas throughout; short inland passage completes Day 2 with no blocking conditions.
High squall risk on Day 2 (active convection likely) and persistent very short wave periods Days 1–3 make for an uncomfortable beat; window is viable but Day 2 squalls are the gate.
A real analysis of an offshore passage, run before departing from Turks & Caicos to Curaçao. The recommendation, the plain-language reasoning, and an interactive Passage Map you scroll through hour by hour. Open it the way you would the morning of departure.
The window we thought we had was gone. When the sun came up, we aborted the passage at 22°N and diverted 358 nm to the Bahamas.
In 2026, on an offshore passage from Florida to Curaçao, we were crossing the Old Bahama Channel on our catamaran when the conditions we'd planned for stopped matching the sea around us. The wind was 25 knots on the nose, the seas stacked to 10–12 ft on our bow as we exited the channel. The only warning was a tugboat captain who hailed us on Channel 16 telling us that the conditions were only going to get worse. We were 18 nm off the northern coast of Cuba with nowhere to hide. The window we thought we had was gone. When the sun came up, we aborted the passage at 22°N and diverted 358 nm to the Bahamas.
When we got home safe, I started pulling apart what I'd missed. The data to know we shouldn't have left the dock existed — but nobody had assembled it for sailors in a form you could read in five seconds. So I built one.
WeatherWindow.AI is what I wish I'd had at 22°N.
Jon Chow, Founder
Your first 3 passages are free on any tier. Run real analyses on real routes before you choose a plan.
For day sails and coastal hops close to home — passages under 100 nm and within eyesight of the shoreline.
You know your local waters — but conditions still change between the marina and the Bay. The Sailor plan answers one question for every departure, in plain language, tuned to your boat: Is today a good day to go?
For weekend cruises and coastal passages — overnight hops and multi-day trips along the coast.
Weekend cruising and coastal passages, where a building breeze, uncomfortable seas, or an afternoon squall can decide your day. One clear go/no-go for the whole trip, tuned to your boat.
For bluewater passages and ocean crossings where it is critical to know whether the forecasts agree or disagree with each other. Plus custom polars, tides, and currents.
Bluewater passages, where getting it wrong means you're 200 nm from the nearest shelter. Captain adds Ensemble Forecasts: 200+ parallel forecast runs across 5 model families, run along your track, so you see which days hold and which are less certain. Plus your own polars and ocean currents on every leg.
No payment required for your first 3 passages, and a 30-day money-back guarantee on your first subscription charge — email billing@weatherwindow.ai to request it. Cancel anytime — renewal charges are non-refundable and run through the end of the current billing period. By signing up you agree to our Terms of Service and Privacy Policy.
No payment is collected now. Subscriptions will auto-renew at the rate for your selected plan until you cancel; cancel anytime from your account once access opens. By joining the waitlist you agree to our Terms of Service and Privacy Policy.
We blend seven atmospheric wind models and four wave models, with per-model weights tuned by forecast lead time. The wind models are ECMWF, ECMWF AIFS, GFS, AI-GFS, UKMO, ICON, and ARPEGE Global. The wave models are ECMWF WAM, GFS-Wave, Meteo France WAM, and GWAM. No single model is right every time. Blending them means one model's error doesn't contaminate your entire forecast — and that matters most past 48 hours, where the forecasts drift apart. On top of that we pull official marine and offshore forecasts from national weather agencies, current synoptic surface analysis charts read by AI vision, and active alerts.
Two ways. Every analysis cross-checks seven wind and four wave models, so you're never reading a single forecast. On the Captain plan, our Ensemble Forecasts go further: 200+ forecast iterations across 5 model families, showing the full spread hour by hour. Where they converge, there is high agreement in the weather models. Where they diverge, you know which days have higher uncertainty so that you can check again before departure or while you're underway.
Other weather apps show you the data. WeatherWindow.AI takes that same data and reads it for your passage. Our Multi-Dimensional Dead-Reckoning Engine runs your boat's polars against the live wind, wave, and current forecasts to project where you'll be hour by hour. It queries the conditions at each of those positions, checks every leg for chokepoints, squall risk, and fuel reserve, reads the synoptic charts from the meteorological agencies, and pulls all of it into one report with a single answer — GO, CAUTION, MARGINAL, NO-GO, or DIVERT — and a plain-language explanation of why. Most weather apps forecast the weather. We forecast your passage in the apparent conditions that your boat will feel.
WeatherWindow.AI isn't a general-purpose AI. We have developed infrastructure to ingest published ensemble models multiple times a day, connect in real time to live weather models, marine forecasts, and synoptic chart analysis. Our app then runs your route through our Dead-Reckoning Engine — placing your boat hour by hour and resolving apparent wind speed, apparent wind angle, heading, and COG at each projected waypoint. The AI reads the output of those calculations and writes them up into a report. A general-purpose AI assistant cannot do any of that.
Yes. Pick your hull type and WeatherWindow.AI applies hull-specific thresholds and motion characteristics. A catamaran behaves differently from a monohull offshore, and the analysis reflects that. You can also upload a custom polar file for the most accurate performance numbers.
Yes. Our Dead-Reckoning Engine models the vessel characteristics that you enter — the hull type, size, and speed profile — and places your boat at each waypoint at the hour you're projected to reach it. It queries the conditions at that exact position, and weighs the risks against your boat's own thresholds. For the sharpest numbers, upload your boat's polar so the engine can compute the most accurate speed over water for a given apparent wind angle and speed. This isn't a regional forecast wrapped up as personalized advice. It's an analysis of your route, your boat, on your timeline.
Up to a 16-day horizon on the Skipper and Captain tiers — long enough to plan an extended bluewater passage. The Sailor tier covers 7 days, the right window for coastal hops and inter-island runs. The spread in wind and wave height across the individual model forecasts shows in the model consensus bar, so you're never planning against a single number that may not hold.
Yes — the forecasts are global. Weather forecasts and surface analysis chart interpretation are available for any ocean basin worldwide. Plan a Caribbean passage, an Atlantic crossing, a Pacific run, or any other passage anywhere.
Passage Reports are built to stay light for bandwidth-limited conditions — a typical one is under 5MB. Your saved passages stay in your account, ready to reopen, and you can print a report to pdf before you lose signal so you have it on hand. If you need a fresh analysis while underway, enter your current GPS position in the Route Map and WeatherWindow.AI re-assesses the remaining legs from where you are. Any saved analysis reflects the conditions at the time it was generated and should not be treated as current — offshore, conditions can change materially within hours.
Your first 3 passage analyses are free — no card required, and no time limit on when you use them. After the 3rd analysis, choose a tier to keep going. Subscriptions are billed at the rate for your selected plan (see Pricing above) and auto-renew until you cancel. You can cancel anytime from your account.
We're opening access Fall 2026. Join the waitlist and your first three analyses are complimentary the day access opens, no payment collected up front. After that, you're billed at the rate for the plan you choose, auto-renewing until you cancel.
The app's work is split three ways. 1) Our source data is grounded from authoritative sources: Forecasts, surface analysis charts, and advisories from international weather agencies covering the Atlantic, Pacific, Indian, and Southern oceans. Our Multi-model wind and wave forecasts originate from models you already use such as ECMWF and GFS, among others. 2) The Multi-Dimensional Dead-Reckoning Engine computes where your boat will be hour by hour and the apparent conditions there. These numbers are calculated by our engine, not by the AI. 3) The AI reads those numbers alongside the source data and writes them up in plain language that you can understand; it writes the recommendation and the reasoning behind it. As with all weather models, forecast accuracy decreases with the time horizon. Beyond 48 hours, the agreement between models widens, and our outputs surface that uncertainty rather than hiding it. You review the raw weather data alongside the conclusion. The Captain makes the final call on every departure decision.
Classic dead reckoning is two-dimensional: it projects where you'll be from your speed and heading. Our Multi-Dimensional Dead-Reckoning Engine fuses live wind, waves, and current with your boat's polars, dimensions, and engine data to compute your projected speed, heading, course over ground, and the apparent wind and waves at every hour. Because it accounts for how the conditions actually change your progress, it projects where your boat will really be — and reads the forecast from there, hour by hour.
No. WeatherWindow.AI tells you what the data says. You decide whether to go. The Captain makes the call — always.
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Run a real analysis on your own route, your own boat, on your own schedule. Your first three passages are free — no card required.
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