、・。
In Singapore, which sits almost directly on the equator, the rainy and dry seasons aren't especially distinct.
Literal
Almost equator-directly-under [at-に] exist Singapore [in/at-では], rainy-season [and-・] dry-season [subject-が] not-very distinct is-not.
A geography-style observation. 赤道直下 ('directly under the equator') is a compact geographical compound — 赤道 (equator) + 直下 (directly below). ほぼ ('almost,' 'approximately') is a register-marked hedge, slightly more formal than だいたい or およそ. The frame ~ある[place][では] ('at/in [place] [topic]') uses では to topicalize a location for a general claim about it — stronger than bare に, and common in expository writing. あまり~ない ('not very,' 'not particularly') is the standard Japanese negation hedge for gradable adjectives. 明瞭 ('clear, distinct') is a Sino-Japanese な-adjective at the upper end of everyday vocabulary.