Carrier route record
WNISP→PBI
Southwest Airlines · Islip to West Palm Beach
- Flights
- 611
- Period
- July 2025 to June 2026
- Share of route
- 50%
- Carriers
- 3
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on ISP to PBI sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 6 points worse than the national rate of 77.6%. The late ones land about 50 minutes behind schedule. That rests on 611 flights, with a median arrival 2 minutes late.
The national on-time rate over the same period is 77.6%, so Southwest on ISP to PBI runs 6 points behind the country as a whole. Across a thousand flights that is about 62 extra late arrivals.
Key figures
On time
71.4%
Arrivals under 15 minutes late, of 598 completed flights
Avg delay
50 min
Across delayed arrivals only, not all flights
Cancelled
1.64%
National rate is 1.81%
Whole route
71.9%
Every carrier on ISP to PBI, 1,223 flights
These figures cover 611 flights between July 2025 and June 2026. On-time means an arrival less than 15 minutes after the scheduled gate time, the same threshold the Department of Transportation uses in its own reports. Cancelled and diverted flights are excluded from the on-time rate and counted separately, which is why the cancellation column matters on its own.
Carrier by carrier
Southwest against every carrier on ISP to PBI
Southwest flew 611 of the 1,223 flights on ISP to PBI, about 50% of it. Its 71.4% on time is about level with the route as a whole at 71.9%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from JetBlue at 72.7% to Frontier at 70.6%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| JetBlue Airways | 541 | 72.7% | 93 min | 2.40% | C |
| Southwest Airlines (this page) | 611 | 71.4% | 50 min | 1.64% | C |
| Frontier Airlinesthin sample | 71 | 70.6% | 86 min | 4.23% | C− |
Departure window
When Southwest runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 28 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am192 flights86.1%
- 8am–11am67 flights84.8%
- 11am–2pm144 flights64.3%
- 2pm–5pm197 flights58.1%
- 5pm–8pm5 flights—
- 8pm–5am6 flights—
Scale runs 50% to 90%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 86.1% of the time, against 58.1% for the afternoon window. That is 28 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 2pm–5pm window is the busiest, with 197 flights scheduled in it.
Across the year
Southwest on ISP to PBI through the year
December is the weak month at 50.8% on time, against 83.9% in October. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. December was the busiest month here, with 64 flights.
Across the week, Friday is the strongest day at 77.9% on time and Sunday the weakest at 66.3%. 12 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Southwest runs late on this route
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 8,534 reported delay minutes.
- 38%Carrier
- 30%National Airspace System
- 29%Late-arriving aircraft
- 3%Extreme weather
The largest share of delay minutes, 38%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 3,233 of the 8,534 delay minutes reported here. The split is drawn from 8,534 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 86.1% on time here.
Cancellations sit at 1.64% against a national 1.81%, which is ordinary. Diversions add another 0.49%.
Connections and stage length
What a delay here costs
5.9% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about 50 minutes, which a normal layover absorbs.
The 1,052 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The return leg runs 72.8% on time across 610 flights, within about a point of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
One caution: this is a thin sample. 611 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking Southwest on ISP to PBI
Put together: treat all of this as provisional. 611 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 71.4% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 598 completed flights over 12 months sit behind that.
Related
Where to go next
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.