Weather Reality Check for a Slow-Moving Seastead

1. Bottom Line Up Front

Your instincts, confirmed Outside hurricane season, on the leeward (south/west) side of the Lesser Antilles, in ordinary trade-wind conditions, your operating environment really is mild: 2–6 ft seas locally, comfortable motion for a semi-submersible-type platform, and plenty of solar. The trade winds are remarkably steady, and the lee of the island chain genuinely works most of the time.

Reality check #1 — the 15-foot ceiling “Never over 15 feet” is not a safe design assumption. Three things break it:

Winter cold fronts (“northers”), Nov–Apr. They roll off North America and hammer the northern islands (Anguilla included) with N–NW winds of 25–35 knots for a day or two at a time. Your “lee” flips: a south-facing shore becomes a windward shore. Exposed water sees 12–18 ft; even partially sheltered spots see wrapped swell of 6–10 ft.
Distant-storm swell. Long-period swell radiates far beyond a hurricane's wind field and diffracts around island ends into the lee. A major hurricane 500–800 miles away can put 10–20 ft swell on exposed coasts and 5–12 ft into places that are “protected.”
Squalls on top of swell. A 35-knot squall line crossing existing 8-ft swell briefly produces steep, confused 12–15+ ft seas with almost no warning.

Treat 15 ft as a typical bad week, not a ceiling. Build and moor for survivability well beyond it.

Reality check #2 — what 1 mph can and cannot do At 1 mph you do not flee storms (they move 10–20 mph); you sidestep them. Three days of warning gives you roughly 65–75 statute miles of repositioning. That is usually enough to dodge the center of a typical, average-sized tropical cyclone if you start early and move perpendicular to its track — but it is not enough to escape the full wind field of a major hurricane, whose tropical-storm-force winds can span 200–300 miles. Your honest strategy is layered: seasonal positioning + early moves (5-day horizon, not 3-day) + island shelter + a platform that survives whatever reaches you anyway.

2. Climate Calendar of the Eastern Caribbean

Season	Winds	Special hazards	Swell situation	Verdict for your route
Dec–Feb	Strongest trades of the year, 15–20 kt typical; “Christmas winds” episodes of 25–30 kt lasting days	Cold fronts / northers reach the northern islands (Anguilla, St. Martin, Virgin Is.) every couple of weeks; N–NW 25–35 kt	Long-period N/NE swell from North Atlantic winter storms; wraps into nominally sheltered water	Fine on the lee side of the chain, but expect several multi-day blow events; do not count on flat water
Mar–Apr	Trades easing slightly	Late-season fronts still possible in March; frequency drops through April	North Atlantic swell season winding down	One of the two best windows; good for longer transits
May–Jul	Moderate trades; more variable	Hurricane season begins Jun 1, but early systems form in the western Caribbean / Gulf, not off Africa. Tropical waves begin arriving every 3–5 days with squalls	Generally settled; occasional southern-hemisphere swell from the SSE far south	Good window, but start watching the NHC 7-day outlook daily from June onward
Aug–Oct	Lighter average trades, but highly disturbed	Peak hurricane season. Cape Verde systems cross the Atlantic along 10–15°N straight at the Lesser Antilles. Rapid intensification is common	Distant hurricanes send 10–20 ft swell hundreds of miles ahead of themselves	Be south of ~12°N (Grenada–Tobago–Venezuela gap–ABC islands) or out of the water entirely. This is non-negotiable for a 1-mph platform
Nov	Trades rebuilding	Hurricane season officially runs through Nov 30; November storms still happen. First cold fronts begin reaching the northern islands	Transition month; both tropical and frontal swell possible	Acceptable late in the month; treat the first half as still-active season

Note on the “southern refuge”: south of roughly 12°N (Grenada southward, the Venezuelan offshore islands, Bonaire/Curaçao/Aruba) direct hurricane strikes become rare — the ABC islands have essentially none on record. But it is a tendency, not immunity: Grenada was devastated by Ivan in 2004 at 12.1°N, and even distant systems send swell and squalls south. Climatology lowers your odds dramatically; it does not excuse you from watching the forecasts.

3. The Lee-Side Assumption: What Holds and What Doesn't

What holds true

The E–NE trades blow roughly 80% of the hours of the year. The south and west sides of the islands are genuinely downwind most of the time, with short local fetch and modest 2–6 ft wind seas.
Your platform type helps: deep slender columns, low waterplane, living space well above the water — this is closer to a mini-semisubmersible than a boat, and it will behave far better in swell than any monohull of similar displacement.

What does not hold true

The lee is direction-dependent. It exists for E–SE trades. A winter front brings N–NW wind and completely reverses which side of an island is sheltered. Any spot you pick must be evaluated for at least two wind quadrants.
Small islands cast a poor swell shadow. Wind waves (short period) stop dead behind an island; long-period swell (10–16 seconds) diffracts around both ends and reflects off shores, filling in the lee. Protection improves with island size and with distance down-drift of the island — the shadow is a wedge, not a wall.
Passages are wind funnels. Gaps between islands accelerate the trades (venturi effect). The Anegada Passage east of Anguilla, the Guadeloupe Passage, the Dominica and St. Lucia Channels — all are notorious for amplified wind and steep, confused seas where swell meets contrary current. Route around them, not through them, when they are blowing hard.
Squalls ignore geography. A fast-moving tropical squall carries 30–40 kt gusts and its own steep wind sea. At 1 mph you cannot dodge one; you batten down and let it pass in 20–60 minutes.

Practical translation Your plan — hop down the chain on the leeward sides, outside hurricane season, with forecasts — is sound and is essentially how the cruising fleet does it under sail. The corrections are: (1) evaluate each anchorage-area for frontal winds too, (2) respect long-period swell wrapping into lees, (3) give passages a wide berth in fresh winds, and (4) accept squalls as routine inconveniences rather than emergencies.

4. Storm Avoidance Math at 1 MPH

Your speed, converted

Lead time	Statute miles traveled	Nautical miles
12 hours	12 mi	10 nm
24 hours	24 mi	21 nm
48 hours	48 mi	42 nm
72 hours (your scenario)	72 mi	63 nm
96 hours	96 mi	84 nm
120 hours (5 days)	120 mi	104 nm
168 hours (7 days)	168 mi	146 nm

How well forecasts actually perform

Approximate NHC track errors (recent-decade averages). The official forecast cone encloses about two-thirds of historical storm centers — meaning roughly one storm in three ends up outside the cone.

Forecast lead	Average track error	Implication for you
24 h	±25 nm	Too late to matter at 1 mph
48 h	±50 nm	Your whole 2-day range is inside the error circle
72 h	±75 nm	Your 3-day dodge distance roughly equals the forecast uncertainty
120 h	±140 nm	Coarse, but it is the horizon where your speed still buys real safety

How big is the thing you're dodging?

Typical named storm: tropical-storm-force winds extend roughly 75–125 nm from center; hurricane-force winds 25–45 nm.
Large major hurricane (Ivan/Irma/Maria class): tropical-storm-force winds 150–250+ nm; hurricane-force winds 50–90 nm.
Forward speed: 8–15 kt in the tropics (roughly 4–6× your top speed), accelerating after recurvature northward.

The uncomfortable arithmetic To be comfortably clear of a typical storm you want to be on the order of 100+ nm from the forecast center; for a major, 150+ nm. Your 3-day range is ~63 nm. Conclusion: a 3-day, 70-mile dodge is a risk-reducer, not a guarantee. It works well when you start near the edge of the threat, move perpendicular to the track, and the storm is average-sized. It fails against large storms, rapidly intensifying storms, and storms that turn toward your escape route. The fix is not more speed — it is starting earlier.

Two asymmetries working in your favor

The dangerous semicircle. For storms moving W–WNW (the norm here), the right-front quadrant (the north side) has the strongest winds and highest seas. Being south of the track puts you on the weak side. Your instinct to head south doubles as storm avoidance geometry.
Swell arrives before the storm. Deep-water swell travels at roughly group speed ≈ 2.56 × period (ft/s). A 14-second swell covers ~500 nm/day. A hurricane 600 nm away announces itself with long-period swell about a day before any wind arrives — free extra warning. Rising swell period with no local wind is a red flag: look east on the satellite imagery.

5. A Playbook That Actually Works at 1 MPH

Position seasonally, not tactically. Aug–Oct: south of 12°N, period. Dec–May: anywhere in the chain you like. Your biggest weather decision is made once a year, not once a storm.
Watch the Atlantic, not just the Caribbean. Systems that threaten the Lesser Antilles are usually visible off Africa 5–7 days in advance. Check the NHC 7-day Tropical Weather Outlook daily from June through November. A wave leaving the African coast today is your 5–7 day heads-up — that is 105–145 nm of movement, which is real avoidance.
Act at 5 days, not 3. Because of rapid intensification (a depression can become a Cat 3 in 24–36 hours in the modern climate), waiting for a 3-day confident forecast often leaves you with too little room. Early moves are cheap; late moves are impossible.
Move perpendicular to the track, biased south. Distance off the track matters more than distance from the storm's current position.
Use big islands as breakwaters. The lee of a large, tall mass (Guadeloupe, Dominica, Martinique, Puerto Rico's south coast) knocks down both wind sea and a useful fraction of swell. Small low islands (Anguilla, Barbuda, the Grenadines) shelter from wind sea only.
Never let a storm get between you and open escape water. Avoid settling into pockets with a lee shore behind you. In every position you occupy, ask: “if a system forms to my east tomorrow, which way do I go, and is that way open?”
Barometer discipline. A fall of 1 mb/hr or more, or a steady slide below ~29.70 inHg, means a system is close enough that forecast debate is over. Execute your plan; do not renegotiate it.
Accept squalls as weather, not emergencies. With Starlink-class connectivity you can watch radar in real time; secure decks, disconnect sensitive electronics, and ride them out. Budget your solar for overcast days — a squally regime can cut PV output 50–80% for a day or two at a time.

6. If You Are Free-Floating (Not Seabed-Moored)

From your description, the cables running between the float bottoms sound like structural cross-bracing of the platform itself rather than seabed mooring lines. If that's correct, then in any serious blow you are a drifting object, and the physics change:

You will drift faster than you can motor. A 30,000-lb platform with a 40×16 ft house on top presents substantial windage above water and very little resistance below (slender columns, small floats). In 35–45 kt sustained winds, expect downwind drift on the order of 1–2 kt — faster than your thrusters. Your mixers will not hold position in a gale; plan for that honestly.
Carry a drogue or sea anchor sized for ~30,000 lb displacement (equivalent to a 45–50 ft sailing yacht; consult manufacturer sizing charts — Para-Tech/Fiorentino/Jordan-series all publish them). Deployed from the leading end, it keeps the platform oriented into the seas, kills most of the drift, and dramatically reduces shock loading on everything.
Choose drift-friendly water. Your ideal storm position is deep open water well clear of lee shores, banks, and reefs, with sea room down-drift. Shallow banks (e.g., the Anguilla/Saint-Martin bank, the Bahamas-style shelves) amplify and break swell — they are the last place a drifting platform wants to be.
If you ever do add seabed mooring, design it for the full storm case (see next section) with scope, elasticity, and chafe protection — taut steel cable to a fixed point in swell is a fatigue and shock-load machine.

7. Engineering Notes: Wind Load, Crest Clearance, Cables

Wind load on the above-water structure

Rough estimate using F = 0.00256 × V(mph)² × Cd × A, assuming ~500 ft² of effective projected area (house walls plus superstructure, Cd ≈ 1.2). Plug in your own numbers:

Sustained wind	Dynamic pressure	Estimated total force
30 kt (squall, common)	~3.0 psf	~1,800 lb
40 kt (gale / strong front)	~5.4 psf	~3,300 lb
55 kt (strong squall / TS fringe)	~10.3 psf	~6,200 lb
70 kt (hurricane fringe)	~16.6 psf	~10,000 lb
90 kt (direct hurricane exposure)	~27.5 psf	~16,500 lb

These are steady-state drag figures; gust factors of 1.3–1.5 apply for peak loads, and any rigging, antennas, railings, or rain-collection surfaces add area. Whatever mooring or drogue philosophy you adopt should be checked against the 70–90 kt row, not the 30 kt row.

Crest clearance

In a sea with 15-ft significant wave height, the highest individual crests run about 0.7 × Hs above still water — call it ~10 ft, with rare extremes beyond that. If your deck sole sits 8–10 ft above the waterline, expect occasional green water on deck in exactly the conditions you're planning to avoid but might not fully avoid. Consequences to engineer for: sealed hatches and windows, drainage that works when submerged, nothing loose on deck, and exterior electrical gear rated for immersion or placed high.

The cables

Chafe is the classic killer of cable systems in swell. Anywhere a cable passes a guide, fairlead, or another cable, motion is constant and slow — perfect wear conditions. Fit sacrificial chafe gear and inspect after every significant event.
Redundancy you've planned is good; also think about what happens dynamically when one element does fail — the load redistributes suddenly, and the survivors take a shock. Some elasticity (snubbers, or a length of chain/nylon in the load path) smooths this out enormously compared to dead-taut steel.
Corrosion at the waterline on permanently wet/dry cycling cable is aggressive in warm tropical water. Over-specify material and inspect on a schedule.
Lightning: an isolated metallic structure in the tropics gets struck eventually. Bond the cable grid deliberately, provide a path to water, and protect electronics with surge suppression.

8. Currents & Eddies: Free Mileage Westbound

The Caribbean Current flows steadily westward through the island passages at roughly 0.5–1.5 kt, fed by the North Equatorial Current. A westbound transit gains a genuine tail-current much of the way — potentially a 30–70% boost to your effective speed at times.
Island-wake eddies exist downstream of larger islands and are real but episodic and poorly charted; treat them as occasional bonuses, not schedule items.
Passage tidal streams can run 1–3 kt and reverse; combined with swell they create the steepest, most confused water in the region. Time any passage crossing for slack or favorable stream, or go around.

9. Forecast Toolkit & Rules of Thumb

Tools

NHC (nhc.noaa.gov) — the authoritative source for tropical systems; read the 2-day and 7-day Tropical Weather Outlooks daily in season.
Windy, PredictWind, PassageWeather — gridded wind/wave forecasts for planning legs.
NOAA/NDBC buoys (ndbc.noaa.gov) — the 41040-series buoys east of the Antilles and 42050-series in the Caribbean Sea give you ground truth on swell period and height; swell period rising is your earliest distant-storm signal.
Chris Parker / Marine Weather Center — Caribbean-focused forecaster serving the cruising fleet via SSB and email; human judgment tuned to exactly your region.
Caribbean Safety & Security Net (SSB, daily) — community weather and safety traffic; verify current time/frequency before relying on it.
Real-time radar via satellite internet — arguably the single biggest safety upgrade for squall awareness available to you.

Cheat sheet

Leave at 5 days, not 3. Your speed makes early cheap and late fatal.
Move perpendicular to the forecast track; south is the weak side of a west-moving storm.
Comfort buffer: 100+ nm from forecast center; 150+ for anything major.
Barometer falling 1 mb/hr: stop deliberating, execute.
Swell period climbing with no local wind: a system is out there — look east.
Aug–Oct: south of 12°N, always.
Never occupy a position with a lee shore behind you.
Engineer the platform for 70–90 kt and 20-ft seas even though you plan to never see them. The plan is avoidance; the design is survival.