Weather Watchers

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Melissa is likely beginning a period of rapid intensification (RI).
Since both the NOAA-P3 and Air Force Reserve C-130 aircraft sampled
the system this morning, the satellite presentation has continued to
improve, with cold -75 to -80 C cloud tops wrapping around the
center with hints of an eye starting to appear on visible images.
The eye is also becoming better defined on radar images out of
Jamaica with an overall diameter of around 20 n mi. In addition, an
earlier GMI microwave pass received after the prior advisory showed
a well-defined cyan ring on the 37-GHz, which is often a harbinger
of RI. Subjective Dvorak intensity estimates were T5.0/90 kt from
SAB, and T4.5/77 kt from TAFB. The objective estimates from UW-CIMSS
were a little lower, but are also quickly rising, and the initial
intensity will be set at 80 kt this advisory, blending these
intensity estimates.

The hurricane now appears to be moving slowly westward, at an
estimated motion of 275/3 kt. A narrow mid-level ridge has built in
to the north of Melissa, and should be the main steering feature
over the next 24-48 hours to help move the hurricane slowly
westward. The deep-layer steering vector still has a slight
southward component, and it wouldn't be surprising to even see a
little south of due west motion occur, like the Google DeepMind
ensembles and ECMWF-AI model have been suggesting in the short-term
forecast. After the next couple of days, the ridging to the north
becomes quickly eroded by a shortwave trough moving across the
southeastern United States. The net result of this changing synoptic
pattern is that Melissa is expected to turn rather abruptly
northward and northeastward by the early to middle part of next
week. Compared to this morning, the track guidance has become more
tightly clustered in the across track direction, and even the 12z
GFS run, which was previous a eastward outlier, is now in better
agreement with the track guidance suite showing a direct landfall in
Jamaica. The main uncertainty is related to the amount of
acceleration that Melissa will undergo after it turns to the
northeast, and there remains large spread in the along-track
direction in both the deterministic and ensemble guidance in the day
3-5 time frame. The NHC track forecast is only slightly more
poleward compared to the prior forecast over the first 12-24 hours,
and convergences very close to the prior track thereafter. This
track is roughly a blend of the latest HCCA and GDMI track guidance.
On this track, this brings Melissa's core near Jamaica early on
Tuesday, and early on Wednesday along the eastern Cuba provinces,
where a hurricane watch is now in effect.

Rapid intensification appears to have started, and assuming Melissa
stays far enough south of Jamaica over the next couple of days,
there appear few impediments to its intensification in the
short-term. Both the hurricane-regional models and the Google
DeepMind ensembles suggest RI could continue for the next 36 to 48
hours. In fact, once again 4/5th s of the latter 50 member ensemble
are forecasting a peak intensity of Category 5 intensity. The 12z
HAFS-A run also showed a peak intensity of Category 5 in 48 hours,
and both HAFS-A/B have been suggesting a similar peak on and off
over the past few days. Given the current trends, the NHC intensity
forecast now shows a 140 kt peak in 48 hours, in general agreement
with this aggressive guidance. Afterwards, some inner-core
oscillations such as eyewall replacement cycles could lead to
fluctuations in intensity before its first landfall in Jamaica. It
is worth stressing that there is very little practical difference
in the overall impacts of a Category 4 or 5 landfall, and
Melissa is expected to be at least that intensity when moves over
Jamaica early next week. Land interaction will likely lead to some
weakening as it moves northeastward across Jamaica, but the storm
will likely also grow in size and is still forecast to be a major
hurricane when it moves over Cuba by the middle of this week. Only
after this period that southwesterly shear begins to increase in
earnest after it moves into the Southwestern Atlantic. The NHC
intensity forecast continues to be on the high end of the overall
guidance, siding with the higher intensity aids such as GDMI (which
has been the best preforming intensity guidance thus far this year)
and HAFS-A, but all the hurricane-regional models show a peak
intensity of at least Category 4 intensity.

Needless to say, there is a very serious situation, in terms of
catastrophic rainfall, wind, and storm surge hazards for Jamaica
and preparations should be rushed to completion in the area
currently under a Hurricane Warning.


Key Messages:

1. Jamaica: A multi-day period of damaging winds and heavy
rainfall is expected to begin tonight, causing catastrophic and
life-threatening flash flooding and numerous landslides. Extensive
infrastructural damage, long-duration power and communication
outages, and potentially prolonged isolation of communities is
likely. A life-threatening storm surge is also likely along
portions of the southern coast early next week. All preparations
should be completed today.

2. Haiti: Catastrophic and life-threatening flash flooding and
landslides are expected across southwestern Haiti into early next
week, likely causing extensive infrastructural damage and
potentially prolonged isolation of communities. Strong winds could
also potentially last for a day or more over the Tiburon peninsula.

3. Dominican Republic: Heavy rainfall could produce catastrophic
flash flooding and numerous landslides in southern portions of the
country.

4. Eastern Cuba, Southeast Bahamas, and the Turks and Caicos:
Monitor Melissa closely. There is an increasing risk of a
significant storm surge, damaging winds, and heavy rainfall by the
middle of next week. In eastern Cuba, the risk of life-threatening
flash flooding and landslides is increasing. A Hurricane Watch is
now in effect for portions of eastern Cuba.
(snip)