What Imereti rain actually looks like
Imereti sits in a humid subtropical belt west of the Likhi Range, and Kutaisi is one of the wettest cities in Georgia. Rain arrives most often from October to April, when a single system can sit over the Rioni valley for two or three days. May and June bring short afternoon thunderstorms instead, usually clearing by evening; July and August are the driest months and your best bet if dry weather matters more than crowds. A local forecast for Kutaisi is more useful than a national one, because the city and the hills twenty minutes east often have completely different weather at the same hour.
Pack for it rather than around it: a light waterproof shell, shoes with grip for wet stone, and a dry bag for a phone. Kutaisi's old streets around the White Bridge and the market side of the Rioni are uneven and slick in rain, and the paving in the park above the fountain drains slowly. If you are driving in from Tbilisi, the 230-kilometre route via the Rikoti Pass takes three to three and a half hours in good weather and longer in heavy rain, so build in slack or consider the train.
Indoor Kutaisi: museums, markets and the cave option
The Kutaisi State Historical Museum on Tsereteli Street is a solid two hours and rarely crowded; it holds archaeological material from the Colchian lowlands and enough context to make the surrounding landscape legible. A short walk away, the Kutaisi Synagogue and the surrounding old-quarter lanes are worth a damp wander under an umbrella. For food, the covered stalls around the central market keep going in rain, and the cheese and spice halls give you something to do while a shower passes. The Bagrati Cathedral hill is exposed, so save it for a break in the weather; the climb is steep and the wind on the ridge is real.
Prometheus Cave near Tskaltubo, about twenty minutes' drive northwest of Kutaisi, is the obvious wet-day set piece and stays a steady temperature year-round. It is an organised visit with a fixed route and lighting, so it works in any weather, and it is busy at weekends. Sataplia, closer to town, pairs a dinosaur-track exhibit with a glass viewing platform that is pointless in low cloud but fine if the rain is light. Book a hotel in central Kutaisi rather than out towards the airport if you want to walk to museums and restaurants between showers.
Tskaltubo, Gelati and the lowland loop
Tskaltubo, the old spa town fifteen kilometres northwest, is the most atmospheric wet-day destination in the region: grand Stalin-era sanatorium buildings, some still in use for mineral baths, set among overgrown parks. Walking it in rain is genuinely good, since the mood suits the place, and the baths themselves are indoor. Allow two to three hours and combine it with Prometheus Cave on the same trip, because they sit on the same road. Skip the long walks on unpaved tracks after heavy rain; the ground turns to clay.
Gelati Monastery, ten kilometres east of Kutaisi, is a working monastery and a UNESCO site with substantial indoor space, medieval frescoes and a view that vanishes in cloud but does not need to be visible to justify the visit. The road up is paved and the drive is under twenty minutes. Motsameta, further along the ridge, is smaller and more exposed, so it is the one to drop in bad weather. If you have a car, a wet-day loop of Kutaisi, Gelati and Tskaltubo fills a day comfortably; without one, taxis for the Gelati run are easy to arrange and the Tskaltubo trip needs a driver for the day.
Where to base yourself and when to book
Base in central Kutaisi for a wet forecast. The blocks between Tsereteli Street, the Rioni and the railway station put museums, the market, cafes and the theatre within walking distance, which matters when every taxi ride is a soaking. Budget and mid-range guesthouses cluster in the old quarter; you will find more choice and better rates outside July and August. Kutaisi's airport on the western edge is served mainly by low-cost carriers, and a taxi into the centre takes roughly twenty minutes, so an early flight does not force you to stay near the terminal.
Booking ahead matters less in Imereti than in Tbilisi or Batumi, with two exceptions: the first week of July, when Kutaisi hosts a large music festival, and the public holidays around Orthodox Christmas in early January. Otherwise a week or two of notice is enough for most of the year. Check that your room actually has heating if you are travelling between November and March; some older guesthouses in converted houses do not, and the damp cold in Kutaisi is more penetrating than the temperature suggests.