HONOLULU (KHON2) - Afternoon soundings show the island atmosphere remains moderately unstable due to the presence of a well-developed low aloft that is centered about 200 miles NE of Oahu. A weak inversion is noted near 8 kft in the PHLI sounding, with moderate instability aloft, while the inversion is absent from the PHTO sounding, with greater instability aloft. Trade wind speeds are below seasonal norms, and have been sufficiently light to allow sea breeze circulations along leeward coasts to move inland, driving the formation of some showery low clouds. The greatest amount of cloud and shower coverage has been over leeward Big Island (where 1-2" of rain fell in localized areas), and interior and leeward portions of Oahu received some rainfall this afternoon as well. Recent radar imagery shows showers developing over leeward Haleakala as well. Meanwhile, visible satellite images show very little in the way of low-level moisture arriving from the E on a gentle to moderate trade wind flow. The forecast anticipates that the trade-wind-supporting ridge N of the islands will remain on the weaker side through tomorrow, then strengthen early next week, with trade winds speeds following suit. With winds remaining light and the atmosphere remaining unstable, an afternoon similar to today's is expected tomorrow. However, since thunderstorms have not been observed the last couple of days, they have been removed from the forecast. Thereafter, typical summertime breezy trade winds will prevail during the upcoming week. The low aloft will move generally W through the weekend, passing N of Kauai on Sunday, then lift N Monday and Tuesday as a strong mid- level ridge builds in from the E. This stabilizing ridge will persist through the week. Until then, the passage of the low will bring the potential for an isolated heavy shower. Limited moisture will keep coverage reduced, but the interior of the Big Island appears most likely Sunday afternoon, and near/over Kauai through Sunday.