I've never even been to Hawaii, but below is a link to a "google doc" from the Cooperative Extension Service at the University of Hawaii that may have some useful info. The plants listed for "Zone 1" in this document are the most wind-tolerant. You would have to "google" each plant to see what kind of sun or shade each one needs, as it doesn't specify light conditions preferred. My feeling is that you'll have the best of luck with a native/indigenous Hawaiian plant, since they will be the best adapted to the wind, salt spray and general climate of beautiful Hawaii. The native plants are the ones with the lower-case "n" next to their names in the document. Here is a link that might be useful: Salt & wind tolerance of landscape plants for Hawaii

@ mangodog: I certainly will keep you in mind. Perhaps cold tolerant is too strong a set of words. Cool tolerant, perhaps with no extreme warmth either. No freezing here (all time low 44F, normal for winter is a 58F). Giving it more thought, I suspect a wind issue is more likely or as gomango suggests pollination. Something unknown happened in 2009 and we had an explosion of mangoes produce. What? The winter was perhaps windier and cooler than the norm so that doesn't seem to be it. Rain seemed pretty consistent so that too doesn't seem to be the trigger. I do suspect our even rains are part of the problem - at least with ones grown so far (again mostly from seed). Either due to pollen intolerant of water or else even rains resulting in a lack of flowering. In this regard, a friend is experimenting with all manner of techniques to induce precocious flowering on trees grown from seed. I will do the same. @ zands: even though our latitude it the same as NC, the GUlf Stream keeps our temperatures evens. And yes, no where in the country can one be more than a mile from the ocean, so plenty of salt spray, though less in inland valleys. Time to reipen doesn't seem to be an issue here. I've seen varieties ripen in August, and fairly large ones at that. I know of some large trees here and would guess all were grown from seed. A friend recently got some Nam Doc, haden, glenn and a few others on the island. Thanks for the suggestions from canaries. Will read up on it some more. Perhaps a better way I should have phrased the topic was for suggestions on mangoes doing well in areas with even rainfall all year... @ gomango: thanks for the tip on indochinese varieties. I am in the hunt for a nam doc mai this summer. And the flower pruning is brand new to me. Interesting. Mind you we rarely drop below 14C for any length of time. The coolest month of the year averages a low of 16C.

"I am imagining a climate like London's" Unfortunately, 900 ft. of elevation in NW Ireland is going to have summers a lot chillier and gloomier than even London's. Look at Derry, for example: https://en.wikipedia.org/wiki/Derry  Summer max average of 66F! They will, however, grow in the climate of the British Isles...it certainly wouldn't have been awarded the AGM if it struggled due to the cool summers. During the ice ages - and that species has survived many - China wasn't covered in ice but it surely had chillier summers. I just expect it to grow somewhat slowly compared to an area with warm, wet summers: for people with smaller gardens, that would actually seem an advantage. In favorable parts of the US, they grow alarmingly quickly. My 'Ogon' (3 ft. to almost 25 ft. in 5 years...and it is slower than the straight species) can easily harden a secondary flush of growth that starts in early September: the amount of warmth and sun I have from mid Sept to mid Nov is probably roughly similar to what the OP gets from mid April to mid October!

some how you live in an area of zone five that has wind that where I grew up in zone 3 and wind coming off the north Dakota prairie, we still could grow things you can't. I know the above sentence is nonsensical, but good grief girl...you are trying to reinvent the wheel with every thing you do, and nothing can possibly grow where you are because you have conditions no one else on the planet has. I've seen it, done it, trumped it...unless you are in a desert, which east of the Mississippi, unlikely. here's one for you...I have references that cite Saybrook Gold Juniper as prone to winter burn. From eastern north Dakota, u of mn, and multiple landscape sources of impeccable repute from the five state area of the upper Midwest (ND, SD, MN, WI, IA), it's perfectly hardy and shows superior resistance to winterburn. So for every source you can show me, I can show you another citing the exact opposite. That's how horticulture is...it's not always as nice and neat as people like to believe. I know people on the North Dakota prairie that don't have the problems you have. You know, that place where two story buildings are built for windloads of 170 mph straightline? Where the governor has a standing order for cancelling school when the temp is colder than -55 degrees. I'll let you ask if it's F or C...that's just cold any way you cut it. What I know about J. chinensis is that wind tolerance is kinda variable and will most likely be hard to discern apart from winterburn. Some cultivars will have winter tolerance to wind and sun in spades, some under certain conditions, some not so much. If you want to know which, you gotta go local. there has to be some local place that's been around forever...even in ottertail county, mn, there's a nursery that's been in operation for over 100 years...there's always a place like that, been around forever, if they don't carry it, or know of it, don't bother. J. virginiana is plenty hardy, all cultivars. IN ZONE FRIGGIN 3. WITH NORTH DAKOTA WIND. prone to turning purple in winter. J. scopulorum is plenty hardy, some variation among cultivars, but don't discolor the way that J. virginiana cultivars can. NOTE: Medora juniper, from the town of Medora, on the north Dakota prairie. Yes, I know I cite ND a lot, but if you have problems with wind and cold and want hardiness above all else, look to what does well under conditions that make any part of western NY look like a walk in a balmy spring breeze. J. scopulorum 'Medora'.