Tropical Storm Pena

000
WTPA44 PHFO 080845
TCDCP4
 
Tropical Storm Pena Discussion Number   7
NWS Central Pacific Hurricane Center Honolulu HI   CP042026
Issued by NWS National Hurricane Center Miami FL
1100 PM HST Sat Nov 07 2026
 
This evening, Pena's vertical coherence appears to be unraveling. On 
GOES-18 satellite, its structure is looking increasingly fragile, 
with the earlier deep convection weakening near the center, with a 
more recent burst primarily east of the center. A 04 UTC WSFM 
microwave pass suggested that Pena has become more vertically 
tilted, with the low-level cloud features on the 37-GHz channel 
indicating the surface circulation running out ahead of the 
mid-level vortex seen on the 89-GHz channel. This was recently 
confirmed by a 0644 UTC ASCAT-B pass, which showed an elongated 
low-level circulation centered east of the deepest convection. The 
peak wind retrieval from the instrument was only 31 kt, though an 
ASCAT-C pass just received had some higher winds. The 06 UTC 
subjective Dvorak estimates from PHFO and PGTW still supported  
45-55 kt, but objective estimates from UW-CIMSS have decreased to 
36-43 kt. Given the rather anemic scatterometer data, the initial 
intensity is lowered to 40 kt this advisory.

The tropical storm's westward motion has slowed a bit over the past 
6 h, with an estimated motion of 270 degrees at 6 kt. A zonally 
oriented low- to mid-level ridge stretches across the Central 
Pacific to the north of Pena. This feature should result in the 
tropical storm maintaining a general westward motion for the next 
2-4 days. However, there is also a prominent low-level westerly-wind 
burst occurring south of Pena resulting in an enhanced monsoonal 
circulation. This feature, combined with a strengthening low-level 
ridge could allow Pena to lose some latitude in 24-60 h. Towards 
the end of the forecast period, the ridge begins to shift eastward, 
which could provide an opportunity for Pena to gain more latitude by 
the end of the forecast, assuming the tropical cyclone is still 
around. The track guidance this cycle is quite similar to the prior 
one for the first 24-36 h, though the better performing track aids 
(HCCA, GDMI, WN3I) now show a more southward track in 36-72 h. Thus, 
the updated NHC track forecast was nudged further south during this 
period once again, blending these more reliable track aids with the 
previous forecast. 
 
Pena's structural degradation this evening makes its intensity 
forecast rather tricky. Environmental conditions appear favorable at 
first glance, with warm 29 C sea-surface temperatures expected along 
the storm's track, and deep-layer shear remaining under 10 kt for 
the bulk of the SHIPS guidance forecast. However, the increasing 
vertical tilt of Pena's vortex appears to be preventing it from 
taking advantage of these favorable environmental conditions, and 
this evening's scatterometer data indicates Pena has weakened from 
earlier today. Another factor worth considering is the monsoonal 
circulation south of Pena, which is producing a lot of convective 
outflow in the path of the tropical storm. Pena is also a rather 
small tropical cyclone, and is likely more sensitive than usual to 
less than pristine environmental conditions. The intensity guidance 
this evening is lower than earlier, with all of the hurricane 
regional models now showing Pena remaining either a weak tropical 
storm or degenerating into a trough of low pressure. The updated NHC 
intensity forecast now shows a little short-term weakening, followed 
by gradual intensification beginning in 36 h. This assumes Pena 
survives, and is able to eventually respond to the more favorable 
environmental conditions. This forecast now leans more on a blend of 
the hurricane-regional model guidance and AI-based guidance, with 
less weight on the statistical-dynamical aids. It is also possible 
Pena dissipates as a tropical cyclone sometime during this forecast 
period, as suggested by the 00 UTC HAFS runs. Needless to say, this 
is a low confidence intensity forecast. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  08/0900Z 11.5N 155.0W   40 KT  45 MPH
 12H  08/1800Z 11.5N 156.3W   35 KT  40 MPH
 24H  09/0600Z 11.5N 158.1W   35 KT  40 MPH
 36H  09/1800Z 11.4N 160.3W   40 KT  45 MPH
 48H  10/0600Z 11.3N 162.5W   45 KT  50 MPH
 60H  10/1800Z 11.1N 164.4W   45 KT  50 MPH
 72H  11/0600Z 10.9N 166.4W   50 KT  60 MPH
 96H  12/0600Z 11.0N 172.0W   50 KT  60 MPH
120H  13/0600Z 12.5N 177.4W   50 KT  60 MPH
 
$$
Forecaster Papin