Tropical Storm Henriette Discussion Number 2
NWS National Hurricane Center Miami FL EP092019
300 AM MDT Mon Aug 12 2019
Deep convection has continued to burst over the western portion of
the cyclone overnight. Although the system is sheared with the
center located near the northeastern edge of the convective mass, a
couple of ASCAT passes have shown a very small area of 30-35 kt
winds over the northwestern portion of the circulation. These
winds extend no more than about 15-20 n mi from the center, but
based on these data the initial wind speed has been increased to
35 kt. Henriette becomes the eighth named storm in the eastern
Pacific basin this season.
The ASCAT data also assisted in locating the center this morning,
and recent fixes show that Henriette continues to move west-
northwestward or 295/12 kt. The tropical storm should move
west-northwestward around the southwestern portion of a deep-layer
ridge that extends westward from northern Mexico. As Henriette
weakens, it is likely to turn westward within the low-level flow.
The updated NHC track forecast is similar to the previous advisory
through 36 hours, but has been adjusted southward at 48 hours to be
closer to the various consensus aids.
Henriette is not anticipated to strengthen much more. Although the
system is predicted to remain over warm waters and within an area of
light to moderate northeasterly shear today, nearby dry mid-level
air is likely to prevent significant strengthening. By Tuesday
morning, Henriette will be moving over cooler waters and into a
more stable airmass. This should lead to weakening, and the
cyclone is predicted to degenerate into a remnant low within
48 hours, with dissipation occurring shortly thereafter.
Tropical Depression Nine-E Discussion Number 1
NWS National Hurricane Center Miami FL EP092019
900 PM MDT Sun Aug 11 2019
The broad low pressure system that the NHC has been tracking the
past several days has finally developed a well-defined surface
circulation and enough organized deep convection to be classified as
a tropical depression. A late-arriving 1716Z ASCAT-C scatterometer
pass indicated the surface wind field was possibly closed at that
time, but since then deep convection with tops of -75C to -80C have
persisted near and to the west of the mid-level circulation center,
suggesting that a low-level center has likely closed off now. Dvorak
satellite intensity estimates are T1.5/25 kt from both TAFB and SAB,
but the initial intensity is set at 30 kt based on 30-31 kt winds
indicated in the aforementioned scatterometer data.
The initial motion is estimated to be west-northwestward or 295/12
kt, based primarily on scatterometer and passive microwave fixes.
The small cyclone is expected to move west-northwestward around the
southern periphery of a deep-layer ridge for the next 3 days until
dissipation occurs. The NHC track forecast lies near the southern
portion of the guidance envelope, between the TVCE consensus model
and the ECMWF-ensemble mean model.
The small cyclone only has about 36 hours to strengthen before the
system moves over sub-26 deg C SSTs. The shear is forecast to be low
at less than 10 kt for the next 72 hours or so, even decreasing to
near 5 kt in 24-36 h, which would normally result in significant
development. However, intermittent intrusions of dry mid-level air
are expected to disrupt the typical intensification process, thus
only modest strengthening is forecast through 36 h, after which
much cooler waters will induce a weakening trend. The official
intensity forecast closely follows a blend of the HCCA and IVCN
intensity consensus models.
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