FRIDAY: 31-JUL-15
(Next Regular WX Update MONDAY – AUG 3)
NOTE: You can follow me on TWITTER @WX_INTEL
(One reason to follow: I Tweet right after posting a New WU Blog)
TROPICAL ATLANTIC - STIRRING – BUT NO BY MUCH!
The Tropics are ‘stirring’ but not by much!
Currently, the only disturbance of note is INVEST 94L now several hundred miles to the WSW of the Cape Verdes, with estimated MAX winds of 20Kts. This system is really entangled up within the ITCZ which has become stronger / better defined over the far eastern ATL on into west Africa. At the same time, and as is typical by this time of year, the SAL has both weakened and remains north of 15˚N latitude. In addition, SST’s are now warm enough to support moderate convection, and according to CIMSS, wind shear near the system has fallen to near 10Kts.
While this more conducive environment for cyclone formation would seem to support some development of 94L, the entanglement with the ITCZ is undoubtedly inhibiting development, as is a generally stable environment just north of the rotational centroid. So while the Specialized Hurricane models still point towards slow development over the next 5 days – the system is likely to encounter more hostile conditions for development as it heads WNW. For this reason, my forecast continues to project ~10% chance for development into a Tropical Storm during the next 5 days.
Upstream from 94L is a more vigorous TW about 2 days away from reaching the African coast. This next system has a somewhat greater chance for development by the end of next week as it moves westward over the eastern ATL as the latest global models call for a major weakening to the SAL, along with a far more benign wind shear environment.
HURRICANE GUILLERMO HEADING FOR HAWAII
While I normally don’t cover Hurricanes outside of the ATL basin – Hurricane Guillermo about 1,800NM SE of the Big Island is worth monitoring – but remains at least 5 days away from becoming any threat to the state.
EVOLVING PATTERN CHANGE REMINISCENT TO JUNE
Both the GFS and ECMWF operational and ensemble models are in very good to excellent agreement on the evolving upper air pattern during the next 10-15 days, with the development of a long wave TROF over the eastern US and a building sub-tropical ridge over the inter-mountain west.
This will bring a slow but steady cool down to the Midwest and much of the east during the week ahead, while well above normal Temps expand and intensify some over the west – a very similar upper air pattern to what existed during much of June.
The cold front marking the leading edge of the cooler and drier air will manage to reach into the SE US westward into TX. However, the main impact for the Gulf coast states will not be cooler Temps – but hotter ones! The drier and far more stable air that will infiltrate into the southern states will bring clear skies during daylight hours, with the stronger solar insolation sending Temps higher than they normally would go during the summer when the air is moist and generally unstable - which normally leads to more afternoon cloudiness - capping the afternoon Temp rise.
Once this pattern becomes established later next week, no major changes are expected to it during Week 2, and possibly into the third week of August as well.
ALASKA – MILD BUT WET PATTERN WILL TURN COOLER IN 8-12 DAYS
With the aforementioned pattern change, we are already seeing rising upper level heights over Alaska, with the main storm track shifting further south, allowing a general warm-up across much of the state during the week ahead. But late next week, a secondary storm track should begin developing over the Arctic Ocean, with surface storms passing just north of the state. And by late Week 2, a more general storm track from near Kamchatka and the Bering Sea eastward into the state will likely lead to a wetter and bit cooler period by mid-month. (All of which is seasonally typical.)
LEARNING ABOUT WEATHER – ONLINE COURSE
A number of people have asked me about any options for ‘online learning’. One of the BEST I know of is the COMET Educational Program offered by UCAR . There are scores of learning modules, with the most recent course addition Introduction to Meteorological Charting
Best of all – it’s free.
**
CLICK IMAGE to open full size image in a new windowFig 1: Color Enhanced IR (infrared) image of the Tropical Atlantic. The main area of interest is in vicinity of INVEST 94L, several hundred miles WSW of the Cape Verdes. The leading TW near 46˚W longitude is moving thru a very stable environment, with the SAL following immediately behind the wave axis. The TW that gave rise to 94L itself has been unable to out run the sudden resurgence in the ITCZ, where a very broad rotation can be seen on the TPW imagery loop (see below). For a variety of reasons, wind flow analysis near/within the ITCZ can be very deceiving, and in reality, tropical cyclones cannot actually form within it. On rare occasions, however, disturbances have been able to migrate far enough away from the ITCZ to develop – but this is both a rare event and virtually impossible to forecast accurately. Just now entering our image view is the strongest T-storm cluster of the season associated with a developing TW. This system is also closely tied with the ITCZ, but model projections do call for the system to eventually move to near the Cape Verdes and then slowly westward by late next week. Something to watch…
Fig 2: The TPW (Total Precipitable Water) Loop (Top) and latest image frame (bottom) highlights areas with deep layered moisture. ‘Bluish’ colors represent dryer air while the darker, ‘orange’ tones highlight areas of deep moisture in the column of air above the surface. The 72 hour looped imagery shows a decidedly strong increase in deep layered moisture within the ITCZ itself over the EATL, with a ‘rotational’ flow observed in vicinity of INVEST 94L.
>Fig 3: Color Enhanced IR (infrared) image focused on INVEST 94L, along with the satellite derived wind shear analysis. The ITCZ is clearly seen extending west-to-east with areas of moderate convection (Cloud top Temps are near -65˚C within some of the heaviest convection – indicating cloud tops of over 50,000ft). Wind shear is a relatively low 10Kts near INVEST 94L, but as mentioned above, automated wind analysis near the ITCZ is often problematic.
>Fig 4: CIMSS SAL analysis (that tends to highlight dry air vs ‘dust’ per se) – with satellite derived low-mid level wind vectors. There is virtually no indication of a low level circulation associated with 94L, though the system remains about 200NM south of the SAL. Model track projections currently track the system closer to the SAL, and any attempts at intensification will be more than offset by dry air entrainment IMO.
Fig 5: Track and Intensity Forecasts from several specialized Hurricane Models that were run early today for INVEST 94L. These models are all used for fairly shallow systems (typical for systems that are weak cyclones or open waves as is the case now). Once again, the built-in biases of these models (especially CLP5 which is a ‘climatologically’ based model) continue to show very slow development over the next 5-days. As noted above, however, it is very unlikely INVEST 94L will ever become a cyclone.
Fig 6: 96 Hour Forecast for Dust Transport Stepping back out to the ‘big picture’, we find dust density within the SAL flow decidedly lower, with a forecast calling for virtually no dust transport at all by early next week! If this forecast pans out – the negative impact of the SAL on the next TW will be insignificant. It remains to be seen, however, if this development is correct and whether it really means the end of ‘SAL Season’ is upon us.
Fig 7: Visible image of Hurricane Guillermo Guillermo, still a week away from being any threat to Hawaii – is estimated to have sustained winds of 80Kts – and will likely attain CAT 2 Intensity within the next 12-36 hrs. Worth keeping an eye on…
Fig 8: GFS Jetstream Forecast for next 2 Weeks. At the beginning of the forecast period, we find the sub-tropical high still centered across the far south central US, with a large TROF across southern AK and GOA, and the developing long wave TROF with its axis now extending from near Hudson Bay Southeastward towards the eastern Great Lakes. By the middle of next week, weak ridging can be seen in vicinity of Alaska, while the eastern TROF will likely de-amplify somewhat as the next short wave TROF out of NW Canada starts digging southeastward towards the Great Lakes – ultimately leading to re-amplification of the eastern TROF during Week2 (around Day 10-12). In addition, by the end of the loop – we see a marked increase in jet stream winds near Alaska along with a developing large upper air Low approaching the NW portion of the state as the sub-tropical high over the US becomes the dominant upper air feature over the lower 48. .
Fig 9: Temperature ANOMALY forecast for Week 1 is based STRICTLY on the MOS data forecasts from the todays 12Z operational GFS model run with minor adjustments towards the raw model data points. Above normal readings across much of the nation as cooler Temps are felt from the northern Plains to upper Midwest and interior Northeast. While still above normal in TX – much drier air will ease the discomfort level there and across the SE. Confidence in the forecast anomaly Pattern and magnitude is solidly above average now, with readings of ‘5’ and ‘4’ on a Scale from 1 to 5 for the anomaly pattern and magnitude respectively.
Fig 10: Running Precipitation totals for US during Week 1 (and only for totals > 0.75”) based STRICTLY on the GFS Heaviest Precip will a likely shift a bit further south across the SE states, while a series of cold fronts will trigger T-storm activity from the Midwest/Great Lakes and Ohio Valley – eastward to the Mid-Atlantic states. A decidedly drier period lies ahead for Alaska.
Fig 11: The Week 2 Temperature ANOMALY forecast is based on the 12Z run of the GFS (70%) integrated with the 12Z GFS Ensemble (30%) using the projected pattern along with explicit surface and 850mb (~5,000 FT) Temp forecasts. Some Temps are adjusted for known / expected anomalous thermal patterns & projected storm system passages.A much cooler pattern over the eastern half of the nation – while well above normal Temps develop across most of the interior West. Confidence in the forecast anomaly Pattern and magnitude is now closer to average by summer standards – with reading of ‘3’ for the overall anomaly pattern, but still only a ‘2’ for the magnitude on a Scale from 1 to 5.
Fig 13: Today’s Temperature anomaly forecasts are based on the 12Z run of the Operational GFS using the GFS MOS data A much warmer period ahead with drier conditions in most areas. Anomalies are likely to remain on the positive side of normal during Week 2 – but not much as cloudiness and more Precip returns to the state.
✭ The Next REGULAR Weather Update will be MONDAY, AUGUST 3 (SOONER if INVEST 94L Develops) ✭
‘Normal’ Summer Update Schedule is MON, WED & FRI - but can vary by a day or so
However, whenever Tropical Cyclones Potentially threaten the US, I’ll be providing Updates 1 or more times per day
Steve
NOTES:
1. A GENERAL Glossary of Weather Terms can be found HERE
2. Another Glossary of weather terms is available HERE
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