CPAC: INVEST 91C

[cycloneye]

Location: 10.0°N 147.9°W
Maximum Winds: 25 kt Gusts: N/A
Minimum Central Pressure: 1008 mb
Environmental Pressure: 1010 mb
Radius of Circulation: 100 NM
Radius of Maximum Wind: 60 NM
-----------------------------------------------
Showers and thunderstorms have increased in coverage associated
with a broad, nearly stationary, area of low pressure, located
approximately 800 miles southeast of Hilo, Hawaii. Environmental
conditions are marginally conducive for development over the next
couple of days. The longer-term chances for development are not as
favorable due to interaction with another area of low pressure
nearby to the east.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 5 days...low...20 percent.

[Kingarabian]

Its structure looks really good. Banding features to the S/SW and to the north of the system. Most of the death shear is located well north of the system so I don't think shear will be a problem here. Air mass in front of is stable though and that may hinder development. I'd give it a 50% chance of becoming a TC due to its proximity to 90C which seems to be the only obstacle in its way.

[Kingarabian]

Per the Euro and the GFS, shear is expected to be favorable. However they show that the dry air will subdue the eventual merger of 91C and 90C. Still early but it looks like Hawaii will be spared as the steering pattern favors a track toward the islands.

[Kingarabian]

ZCZC HFOTWOCP ALL
TTAA00 PHFO DDHHMM

Tropical Weather Outlook
NWS Central Pacific Hurricane Center Honolulu HI
200 PM HST Tue Aug 15 2017

For the central North Pacific...between 140W and 180W:

1. Showers and thunderstorms continue to develop in association with
a broad area of disturbed weather around 900 miles southeast of the
Big Island of Hawaii. Two weak lows are currently identified within
this area, but conditions are not conducive for both to develop.
However, development of a single low is possible over the next
couple of days as it drifts slowly toward the northwest.
* Formation chance through 48 hours...medium...40 percent.
* Formation chance through 5 days...medium...60 percent.

Elsewhere, no tropical cyclones are expected during the next 5 days.

Forecaster TS

[Kingarabian]

18z HWRF has a modest TS.

[Kingarabian]

Looks like 91C's vort already has a closed and defined LLC per this latest SSMIS pass:



Needs to fire and maintain deep convection and it'll be classified.

However 90C is firing a lot more convection, and 90C's convection is considerably colder. So since 90C is firing off deeper convection, I think the consolidation will happen here and it will pull 91C's circulation to it.

00z Guidance shows a pretty moderate TC coming out of 91C's vort.

[Yellow Evan]

Pretty sure this is off the TWO.

[Kingarabian]

Still on the Navy sites and SSD:



Based on that mcirowave pass, it's pretty much a tropical depression right now.

Though I doubt Birch, Houston, and Co want to stay up till 11PM and 5AM to issue to advisories on a tropical depression that will likely have no impact.

[Yellow Evan]

TXPN43 PHFO 171809
TCSNP3

CENTRAL PACIFIC TROPICAL CYCLONE SUMMARY - FIXES
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI
1810 UTC THU AUG 17 2017

A. TROPICAL DISTURBANCE 91C (SE OF HAWAII) CP912017.

B. 17/1730Z.

C. 12.3N.

D. 148.5W.

E. GOES15.

F. TXX/XX/XX.

G. VIS/IR/EIR.

H. Remarks: LLCC AT FIX POSITION IS DIFFICULT TO FIND AND MAY BE A TROUGH. THIS SYSTEM IS TOO WEAK TO CLASSIFY.

I. ADDL POSITIONS NONE.

$$

POWELL.

[Kingarabian]

Looks like 91C beat out 90C as 90C is dropped.





Probably close to a TS right now.

[Yellow Evan]

1. Thunderstorms associated with a low about 600 miles southeast of
Hilo, Hawaii have intensified over the past several hours. However,
over the next few days, the low will be moving into an area where
the environment will be increasingly hostile. Dry air and
strengthening southwest winds aloft are forecast to cause the low
to dissipate by the middle of next week.
* Formation chance through 48 hours...low...30 percent
* Formation chance through 5 days...low...30 percent

[Kingarabian]

They'll probably up the chances or classify it if it maintains this deep convection for another 5-6 hours.

[Yellow Evan]

:uarrow: They'll probably up the chances or classify it if it maintains this deep convection for another 5-6 hours.

I'm not sure if this will ever be classified, given that CPHC/SAB isn't issuing T numbers. In theory has 24 hours left though.

[Kingarabian]

:uarrow: They'll probably up the chances or classify it if it maintains this deep convection for another 5-6 hours.

I'm not sure if this will ever be classified, given that CPHC/SAB isn't issuing T numbers. In theory has 24 hours left though.

I'm confused on why not. Looks like a 1.0/1.5

[Kingarabian]

[Kingarabian]

ZCZC HFOTWOCP ALL TTAA00 PHFO DDHHMM
Tropical Weather Outlook

NWS Central Pacific Hurricane Center Honolulu HI 200 PM HST Fri Aug 18 2017

For the central North Pacific...between 140W and 180W:
1. Thunderstorms associated with a low about 550 miles southeast of Hilo, Hawaii have weakened over the past several hours. The low low is moving northwest very slowly. Over the next few days, the low will be moving into a more hostile environment. Dry air and strengthening southwest winds aloft are forecast to cause the low to dissipate by the middle of next week.

* Formation chance through 48 hours...low...30 percent * Formation chance through 5 days...low...30 percent Elsewhere, no tropical cyclones are expected during the next 5 days. Forecaster

Donaldson


How does this only have a 30% chance? How has convection weakened?