New Orleans receives more precipitation than Seattle on fewer wet days. So do Houston and Charleston. The revealing part is not merely the larger annual total. It is what happens when the rain arrives: days that accumulate at least an inch are much more common at all three southern airports.
That is a useful distinction if “rainy” means a long sequence of damp interruptions to you, but something else if it means a sudden downpour overwhelming an outdoor plan. The cities are not exchanging the same weather in different quantities. They distribute their water differently across the year and across individual days.
Four Airports, One Measuring Stick
This comparison uses NOAA's 1991-2020 normals throughout. A wet day means at least 0.01 inch, or 0.254 millimeter, of precipitation. A one-inch day means at least 25.4 millimeters. These are daily accumulations, not hourly rainfall rates. Precipitation includes the liquid equivalent of snow.
| Airport station | Precipitation | Days ≥0.01 in | Days ≥1.00 in |
|---|---|---|---|
| Seattle-Tacoma | 39.34 in / 999 mm | 156.2 | 5.6 |
| Houston Intercontinental | 51.84 in / 1,317 mm | 104.4 | 15.5 |
| New Orleans International | 63.35 in / 1,609 mm | 115.1 | 20.1 |
| Charleston International | 52.51 in / 1,334 mm | 113.7 | 15.7 |
Source: NOAA annual normals, stations USW00024233, USW00012960, USW00012916 and USW00013880. Airport records represent reference locations, not every neighborhood. Millimeters are rounded.
Sea-Tac has the most measurable-precipitation days and the fewest one-inch days. New Orleans has about 41 fewer wet days a year, yet more than three times as many one-inch days. The contrast is not a matter of counting mist in one city and downpours in another: both thresholds are identical across the four records.
Another way to read the columns is to divide one-inch days by wet days. The result is about 4% at Sea-Tac, 15% at Houston, 17% at New Orleans, and 14% at Charleston. This calculation is a compact description of the normals: a substantially larger fraction of southern wet days reaches the higher threshold.
The Average Wet Day Is Not the Typical Storm
Dividing annual depth by annual wet-day count gives another illustrative ratio: roughly a quarter-inch per counted wet day at Sea-Tac, compared with around half an inch at Houston and New Orleans. Charleston sits a little below half an inch. It is a useful way to picture the contrast, but it is not a storm forecast or the median amount you should expect when rain starts.
A few very wet days can pull an average upward. Daily records also do not say whether an inch fell in one hour or across most of a day. The one-inch counts establish heavier daily accumulation; they do not establish a universal “quick shower, then sunshine” schedule.
The atmospheric ingredients help explain the difference. The National Weather Service identifies moisture, instability, and lift as the basic requirements for thunderstorms, with warm tropical waters an important moisture source. That provides a mechanism for substantial accumulations in the Gulf and Southeast. It does not mean every southern rain event is a thunderstorm, or that Seattle never experiences heavy rain.
The Southern Cities Do Not Share One Rain Calendar
New Orleans and Charleston have a pronounced summer contribution. At New Orleans International, June through August total 21.32 inches, about 34% of the annual normal. At Charleston International, those months total 19.78 inches, about 38%. Sea-Tac receives just 3.02 inches in the same three months, about 8% of its annual total.
Houston is a useful complication. Its June-August total is 14.61 inches, about 28% of the year, and its October normal, 5.46 inches, is wetter than either July or August. The comparison is not simply “Seattle has winter rain; the South has summer rain.” Houston's wetter months are more spread out.
For someone choosing among the southern cities, this is more useful than the shared fact that all three exceed Seattle annually. Charleston and New Orleans place a larger share of their water in the summer quarter. Houston supplies an example where substantial rainfall is less concentrated in that particular season. A move among them changes the pattern, not just the total.
Water on the Ground Is a Separate Comparison
A high annual total does not identify a flooded street. The speed of a particular storm, the ground already being wet, and the places available for water to go all matter. The National Weather Service's flash-flood guidance distinguishes storm duration and rainfall production from the conditions of the receiving landscape.
This is why the table should influence expectations without becoming an address-level risk score. It supports taking larger daily accumulations seriously in Houston, New Orleans, and Charleston. It cannot tell you which house, basement, road, or waterfront block will flood, and it should not be sold as a substitute for that investigation.
Nor do fewer wet days prove more sunshine. A dry day can be cloudy, and a wet day can have long bright intervals. The appealing postcard and the high precipitation total can both be real without one cancelling the other.
Compare Houston and New Orleans for the Gulf contrast, or Charleston and New Orleans for two summer-wet coastal choices. Seattle is the useful benchmark because it exposes the ambiguity in the word “rainy.” It wins the count of wet days here. The southern cities put more water into fewer of them.
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