Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
442 AM EDT Sun Apr 12 2026

Valid 00Z Mon 13 Apr 2026 - 00Z Mon 20 Apr 2026

The closed upper low currently situated approximately 1000 to 
1100 miles to the northwest of the Islands near 36N 167W, will 
remain nearly stationary through late Monday, and then only begin 
to push slowly eastward Tuesday and Wednesday. There is no change 
to prior model consensus of mid to upper level southwesterly to 
west southwesterly flow aloft remaining established across the 
islands, on the southeast side of this nearly stationary closed 
low. This will allow and axis of much above average PW values, 2 
to 4+ standard deviations above the mean to persist across the 
Island chain through much of next week.

Shortwaves in this persistent southwest mid to upper level flow 
will continue to enhance large scale uvvs in the anomalous PW 
axis, supporting potential for localized  heavy rainfall and an 
elevated risk of life threatening flash flooding and 
mudslides/debris flows into early week.  While the anomalous PW 
axis is expected to remain across the Islands through much of the 
upcoming week, models continue to be more emphatic about heavy 
rain chances through the weekend and Monday, primarily for the
western portion of the Islands.  After this, model qpf is not as 
focused, with Kauai having the greatest precip chances into mid
week. However,locally heavy rains are still possible elsewhere, 
given the much above average PW values remaining across the state 
and potential for additional shortwaves in the above mentioned 
west southwesterly to southwesterly mid to upper level flow. 

Toward the end of the forecast period, there are indications that
a new mid to upper level low may form to the west of the Islands
along approximately 165W - 170W and to the south of 30N. There is
a lot of spread, at the moment with this trof evolution. One thing
that is in common, however, is that this potential next trof will
not be as strong as the current one that is well north of the 
Islands. Low confidence on any solution, with a large spread in 
the global guidance. The UK and CMC have a farther southwest 
solution, while the GFS and EC are farther to the northeast. The 
AIGFS is more in line with the farther southwest UK and CMC 
solutions and would favor increasing precip chances for the 
western Islands toward the end of the forecast period, while the
GFS and EC solutions would be less favorable.

Through much of the forecast period, the typical trade wind 
pattern will remain disrupted. A return to a more normal trade 
pattern may occur late in the upcoming week as surface high 
pressure builds to the north at the same time the potential new 
mid to upper level low forms to the west of the Islands.

Oravec