The year on the coast, with the chapada alongside
The scoring is for a trip to Bahia as a whole. The main figures are Salvador's and, for each month, what that same month is doing in Lençóis, 410 kilometres inland, is added. They almost never agree.
There is an automatic reflex when planning a trip to north-east Brazil: look at the temperature, confirm that it is warm all year and conclude that it does not matter when you go. The first half of that reasoning is correct. The second half is what ruins trips.
In Bahia the deciding variable is not the thermometer: it is rain. And rain does two surprising things here. The first is that the coast's wet season falls in the southern winter, the opposite of almost the whole country. The second is that, four hundred kilometres inland, that season flips.
01 Temperature is of no use to you
Look at Salvador's average highs across the year: 31.0 in January, 31.1 in February, 30.9 in March, 29.6, 28.1, 27.1, 26.6, 26.7, 27.7, 29.1, 29.8 and 30.6. The whole year's range is four and a half degrees.
The lows do the same: they run from 21.0 to 24.1 degrees. No month drops below twenty-one at night and no month passes thirty-one by day. It is a tropical rainforest climate, with average humidity around 81%, and its defining feature is that it has no thermal seasons.
That is why a temperature table does not help you choose. What separates one month from another here is how many days it rains and how many hours of sunshine are left: from 234.8 hours in January to 144.6 in June, almost ninety hours of difference inside the same year.
02 On the coast, winter is the wet season
Salvador's wet block runs from April to July: 284.9, 302.2, 237.6 and 194.1 millimetres. Four consecutive months above 190, with 16, 18, 19 and 18 rainy days respectively. In June it rains almost two days in every three.
The dry block is the opposite and coincides with the southern summer: December, 63.4 millimetres over 7 days; January, 76.9 over 9; October, 91 over 8; November, 108.2 over 8. Four months in which it rains barely a week each.
This contradicts the pattern many people bring from other parts of Brazil, where summer brings the storms and winter dries out. Here it works the other way round, and anyone booking on the southern calendar will find May, June and July underwater.
03 Four hundred kilometres and the calendar flips
Lençóis, the gateway to the Chapada Diamantina, is 410 kilometres from Salvador. Its climate is no longer rainforest but savanna, with a marked wet and dry season, and it adds up to around 1,058 millimetres a year against the coast's 1,833.3.
But the striking thing is not the total: it is the distribution. Its wettest month is March, with 164.3 millimetres, followed by November with 135 and January with 133.1. Its driest is September, with 26.4. July and August stop at 41.5 and 40.4.
Lay the two series on top of each other and you get a mirror. In May the coast takes 302.2 millimetres and the chapada 62.5: almost five times less. In December the coast takes 63.4 and the chapada 115.8: almost double. The two calendars cross and separate without ever quite agreeing.
04 What that does to the waterfalls
The chapada is a massif of eroded sandstone, and its greatest draw is its waterfalls. The problem is that a waterfall is a river, and a savanna river does not carry the same flow in March as it does in September.
From this comes a contradiction worth understanding before booking. The months when the chapada walks best, June to September, with between 26 and 56 millimetres a month, are exactly the ones when least water comes down. And the months of full flow, November to March, are the ones of mud and storms.
The middle ground is November. With 135 millimetres the interior has already had enough water for the rivers to run again, but the season has not yet closed in, and on the coast November gives 108.2 millimetres spread over just 8 days.
05 And what it does to the nights
There is a second difference between the two Bahias that has nothing to do with rain and everything to do with altitude, and you notice it at bedtime. In Salvador the year's lowest average minimum is 21.0 degrees, in August. In Lençóis, in July, it is 16.6.
Four and a half degrees of difference at night, in a humid climate, is not a nuance: it is the difference between sleeping with a fan and sleeping with a blanket folded at the foot of the bed. And by day the interior is hotter, not cooler: average highs of 31.8 degrees in February against the coast's 31.1.
The year's four stretches
Between 194.1 and 302.2 millimetres a month in Salvador, with 16, 18, 19 and 18 rainy days, and sunshine at its 144.6-hour minimum in June. Inland the opposite happens: July leaves 41.5 millimetres in Lençóis. If the trip is a coastal one, this is the block to avoid.
The coast falls from 129.7 to 99.3 millimetres and recovers 205 hours of sunshine; the chapada touches its annual low with 40.4 and 26.4. It is the best moment for walking inland and the worst for seeing water fall: the rivers are at their lowest.
On the coast, 91, 108.2 and 63.4 millimetres over 8, 8 and 7 days, with more than 200 hours of sunshine a month. On the chapada, 75.5, 135 and 115.8: the rivers carry water again. It is the only stretch when both halves of the state work at once.
The coast stays relatively dry in January, 76.9 millimetres, and turns wet in March, 147.3. The interior is in full season: 133.1, 93.9 and 164.3, its annual maximum. Good beach days and a chapada with difficult trails.
06 The month that works for both
If the trip is coastal only, the answer lies between October and January, and inside that window December is the year's driest month, with 63.4 millimetres spread over seven days. It is also the busiest and most expensive, so November usually comes out better for the same sky.
If the trip is chapada and walking only, the answer is the June to September block, with 55.7, 41.5, 40.4 and 26.4 millimetres. Dry trail, nights of 16.6 degrees and no afternoon storms. In exchange, the waterfalls will be thin.
And if the trip wants both Bahias, which is what almost everyone ends up wanting, the calendar's one clean answer is November. The coast gives 108.2 millimetres over eight days and 202.9 hours of sunshine; the interior has already taken 75.5 in October and adds 135 that month. It is the point where the two curves, which spend the year dodging each other, touch.
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