Map from Google - Guadeloupe

In Guadeloupe, the climate is tropical, hot and humid all year round, with a relatively cool and dry season from January to mid-April, called carême (Lent), and a hot, humid and rainy season from mid-June to mid-November, called hivernage (whose root reminds of the winter, although it is a hot season, and also quite sunny). In the former period, the northeast trade winds, constant winds typical of tropical climates, blow steadily and with moderate intensity, while in the latter period the winds are more irregular, and may have some breaks, increasing the feeling of sultriness. Between them there are two transitional periods: from mid November to early January (when the northeast wind starts to blow, the temperature decreases a bit and the weather gets better), and from mid-April to Mid-June (when both the temperature and the frequency of downpours gradually increase).

Guadeloupe is an island, overseas region of France, actually formed by two islands that are connected with each other: Basse-Terre (the western island, where the regional capital of the same name is located) and Grande-Terre. In addition to these, we find some smaller islands: Marie-Galante, the small group of Iles des Saintes, and La Désirade.

Here are the average temperatures of Pointe-à-Pitre, located in the westernmost part of Grande-Terre, where also the airport is located. As you can see, there are little variations between the coolest and the warmest period.
Average temperatures - Pointe-à-Pitre
Pointe-à-PitreJanFebMarAprMayJunJulAugSepOctNovDec
Pointe-à-PitreJFMAMJJASOND
Min (°C)202020222324242423232221
Max (°C)292929303131323232313030
Min (°F)686868727375757573737270
Max (°F)848484868888909090888686

Rainfall in Guadeloupe varies greatly in quantity depending on the area, but follows the same pattern, and are more frequent and abundant from May to November (and especially from July to November), and less frequent and shorter from December to April (and particularly in February and March).
In Pointe-à-Pitre, more than 1,800 millimetres (70 inches) of rain fall annually, of which more than 100 mm (4 in) per month from April to December, and more than 200 mm (8 in) from July to November. The driest month is February, with an average of 60 mm (2.4 in). Here is the average rainfall in Pointe-à-Pitre.
Average precipitation - Pointe-à-Pitre
Pointe-à-PitreJanFebMarAprMayJunJulAugSepOctNovDecYear
Pointe-à-PitreJFMAMJJASONDY
Prec. (mm)8565751251501201502002352302201351780
Prec.(in)3.32.634.95.94.75.97.99.39.18.75.370.1
Days151212121413151617181716175

In inland areas, the island of Basse-Terre is more humid and rainy, because of the volcano Grande Soufrière, 1,467 metres (4,813 feet) high: along its slopes the sky is often cloudy, and the climate is equatorial, that is, humid and rainy all year round, in fact a rainforest grows there. On the summit of the vulcano, nearly 10 meters (394 inches) of rain per year fall, and it rains almost every day (340 days a year). On the other hand, the small islands, being flat, receive a relatively small amount of rain, so that the total drops to about 1,200 mm (47 in) per year. Even in the northern and eastern part of Grande-Terre (see Port-Louis, Anse-Bertrand, Le Moule, Saint Francois, Sainte-Anne), rainfall is not very abundant, and amount to around 1,300 mm (50 in) per year.
The rains occur throughout the year as downpours or thunderstorms, maybe intense, but which generally do not last long, and therefore do not reduce too much the sunshine hours, though sometimes there may be a more intense wave of bad weather.
The greatest danger comes from and tropical storms and cyclones, called hurricanes in the Caribbean area, which may pass from June to November, but are most likely from August to October. A very violent hurricane that hit Guadeloupe was Hugo, on September 17, 1989.

Guadeloupe

The sea is warm enough for swimming all year round, as we can see from the following table.
Sea temperature - Guadeloupe
GuadeloupeJanFebMarAprMayJunJulAugSepOctNovDec
GuadeloupeJFMAMJJASOND
Sea (°C)272626272728282829292827
Sea (°F)817979818182828284848281

When to go

The best time to visit Guadeloupe goes from January to March, being the coolest and driest. In December and April, which are usually acceptable months, the rains can sometimes be abundant. In the period May-October there's a humid heat; there is no shortage of sunshine, but showers and thunderstorms are frequent, and sometimes abundant, especially in the second part, from August to October, when in addition the risk of hurricane rises.

What to pack

All year round: light, tropics-friendly clothing, sun hat, sunscreen, possibly a light sweatshirt and a light raincoat for thunderstorms. From December to March, a light sweatshirt for the evening.
For the reef, equipment for snorkeling, water shoes or rubber soled shoes.
Sweatshirt, raincoat and hiking boots for hiking in La Grande Soufrière.