TC 06P rapidly developed clipping Northen VITI LEVU within 12h// TC 05S//3 Week TC Formation Probability//2909utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON 06P. 3HOURLY SATELLITE BULLETINS ARE ISSUED ON 05S AND 90S.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE (TC) 06P (SIX) HAS TRANSFORMED AT AN INCREDIBLE PACE FROM A 30 KNOT ILL-DEFINED CIRCULATION EMBEDDED WITH THE SPCZ, TO A STRONG TROPICAL CYCLONE WITH A MICROWAVE AND RADAR EYE FEATURE. POST-ANALYSIS SUGGESTS THAT THE 290000Z INTENSITY WAS VERY LIKELY WELL ABOVE 35 KNOTS BUT A LACK OF DATA, THE VERY SMALL NATURE OF THE SYSTEM AND THE OVERALL WEAK APPEARANCE IN VISIBLE AND INFRARED SATELLITE IMAGERY PRECLUDED ASSESSING IT AT A HIGHER INTENSITY AT THAT TIME. A 290158Z AMSR2 MICROWAVE PASS CHANGED ALL THAT IN AN INSTANT, WHEN IT REVEALED A CLEAR, VERTICALLY ALIGNED MICROWAVE EYE IN BOTH THE 89GHZ AND MOST STRIKINGLY IN THE COLOR ENHANCED 36GHZ IMAGE. A QUICK GANDER AT THE RADAR DATA OUT OF NADI, CONFIRMED THE SYMMETRIC AND ALIGNED NATURE OF THE VORTEX, WHICH CONTINUED TO BECOME BETTER DEFINED. BASED ON THE RADAR DATA, THE SYSTEM LIKELY REACHED PEAK INTENSITY AROUND 0400Z-0500Z. BY 290600Z THE CENTER WAS PASSING VERY CLOSE TO WAYASEWA AND KUATA ISLAND, MOVING EASTWARD AT ABOUT 14 KNOTS. THE RADAR DEPICTION HAS BECOME INCREASINGLY RAGGED SINCE THE 0500Z PEAK. THE MSI AND ENHANCED INFRARED (EIR) IMAGERY HAVE NEVER SHOWN A CLEAR EYE, THOUGH THERE WAS BRIEFLY A WARM SPOT IN THE BD-ENHANCED EIR. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE RADAR EYE FEATURE. THE INITIAL INTENSITY IS ASSESSED WITH LOW CONFIDENCE, AS THE SMALL SIZE OF THE SYSTEM IS PRECLUDING ACCURATE DVORAK-BASED INTENSITY ESTIMATES AND CIMSS OBJECTIVE ESTIMATES ARE NOT YET AVAILABLE, MEANING THE INTENSITY ASSESSMENT IS BASED ALMOST ENTIRELY ON THE APPEARANCE OF THE SYSTEM IN THE MICROWAVE IMAGERY. THE ENVIRONMENT IS GENERALLY FAVORABLE, WITH WARM SSTS, LOW VWS AND MODERATE POLEWARD OUTFLOW.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TC 06P IS FORECAST TO TRACK GENERALLY EASTWARD, WITHIN A LOW PRESSURE TROUGH WHICH LIES ON A GENERAL WEST-EAST LINE FROM FIJI TO NIUE AND THEN SOUTHEAST TO THE COOK ISLANDS. ADDITIONAL STEERING PRESSURE WILL BE APPLIED BY THE DEEP-LAYER NER SITUATED TO THE NORTHEAST. THE SYSTEM WILL CLIP THE NORTHERN COAST OF VITI LEVU OVER THE NEXT 12 HOURS, THEN TRACK EASTWARD THROUGH THE NORTHERN PART OF THE LOMAIVITI GROUP AND THE NORTHERN AND CENTRAL LAU GROUPS OF ISLANDS WITHIN THE FIRST 24 HOURS OF THE FORECAST. AFTER TAU 36 TC 06S IS FORECAST TO TURN MORE SOUTHEASTWARD TOWARDS THE VAVA'U GROUP OF TONGA. THE EXTREMELY SMALL SIZE OF TC 06S HAS ALLOWED IT TO THRIVE IN AN ENVIRONMENT WHICH IN GENERAL WOULD NOT BE EXPECTED TO SUPPORT RAPID INTENSIFICATION. UPPER-LEVEL WINDS ARE IN GENERAL FROM THE WEST, BUT THE MOST RECENT CIMSS ATMOSPHERIC MOTION VECTOR (AMV) ANALYSIS SUGGESTS A SPLIT IN THE FLOW, JUST UPSTREAM (WEST) OF THE CORE OF TC 06S, SUGGESTING THAT THE LOCALIZED SHEAR DIRECTLY OVER TC 06S IS ACTUALLY EVEN LOWER. AND WHILE OUTFLOW IS MOST PROMINENT TO THE SOUTH, THE SPLIT FLOW HAS PROVIDED A BIT OF AN EQUATORWARD OUTFLOW CHANNEL AS WELL. THE SYSTEM ALSO CURRENTLY SITS IN A SMALL POCKET OF DEEP MOISTURE, THOUGH EXTREMELY DRY AIR IS LURKING JUST TO THE SOUTH AND WEST. THESE CONDITIONS ARE NOT EXPECTED TO LAST MUCH BEYOND THE NEXT 12 HOURS, WITH ALL AVAILABLE MODEL DATA SUGGESTING AN INCREASE IN SHEAR AND A SHARP DRYING IN THE MID-LEVELS AS THE SYSTEM MOVES EAST OF VITU LEVU. THE SYSTEM IS THUS EXPECTED TO MAINTAIN INTENSITY AS IT SKIRTS ACROSS THE NORTHERN COAST OF VITU LEVU, THEN BEGIN A STEADY WEAKENING TREND, DISSIPATING AS A TROPICAL CYCLONE WITHIN 36 TO 48 HOURS.

MODEL DISCUSSION: MODEL DATA IS EXTREMELY LIMITED, IN THE SENSE THAT THE ONLY MODEL THAT HAS PICKED UP ON TC 06S IN ANY MEANINGFUL WAY IS THE HWRF AND EVEN IT DID NOT INDICATE THE EXTREMELY RAPID INTENSIFICATION SEEN OVER THE LAST 6 HOURS. HOWEVER, FROM A TRACK PERSPECTIVE, THE GLOBAL MODELS DO IN GENERAL SEEM TO HAVE A GOOD HANDLE ON THE SYSTEM TRACKING TOWARDS THE EAST THEN TURNING SOUTHEAST BY TAU 48. THE GFS HOWEVER, LOSES THE VORTEX COMPLETELY, NOT REALLY HAVING A VORTEX TO BEGIN WITH, WITHIN THE FIRST 12 HOURS. THE ECMWF, HAFS-A AND HWRF AND UKMET ARE IN STRONG AGREEMENT WITH THE JTWC FORECAST TRACK, BUT CONFIDENCE REMAINS MEDIUM DUE TO THE FACT THAT THE MODELS ARE NOT INITIALIZING WELL AND THUS OUTPUT IS LIKELY QUESTIONABLE. IN TERMS OF INTENSITY, AS NOTED ABOVE, THE ONLY MODEL THAT HAS SHOWN ANY SORT OF SKILL IN DEPICTING A MODERATELY STRONG VORTEX IS HWRF. IN THE FORECAST, HWRF SHOWS THE SYSTEM WEAKENING JUST AS RAPIDLY AS IT DEVELOPED, REACHING 30 KNOTS WITHIN 12 HOURS. THE HAFS-A AND COAMPS-TC MEANWHILE WEAKEN THE SYSTEM AT A SLOWER PACE. THE TRUTH LIKELY LIES SOMEWHERE BETWEEN, AND THE JTWC FORECAST IS A BLEND OF THE DETERMINISTIC OUTCOMES, THOUGH THE FORECAST IS HIGHER THAN THE GUIDANCE THROUGH TAU 24. CONFIDENCE IS LOW IN ALL ASPECTS THROUGH THE FORECAST PERIOD.

Recent observations indicate that the intraseasonal Madden-Julian Oscillation (MJO) remains active. Interference from both the low frequency base state and equatorial Rossby wave activity over the Maritime Continent have slowed the eastward propagation of the MJO signal considerably during the past two weeks. In fact, the CPC upper-level velocity potential based index reflects westward movement since mid-December due to the robust Rossby wave projection. Both a potentially developing La Niña event across the central Pacific and an unusually late negatively phased Indian Ocean Dipole (-IOD) event are contributing to a low frequency enhanced convective signal over the Maritime Continent, with a Rossby wave constructively interfering, while the MJO is currently propagating across the Pacific with destructive interference from the base state. Dynamical model MJO index forecasts show a fairly fast transition from the slowly propagating index to a signal over the east-central Pacific. Additional Rossby wave activity over the East Pacific, likely driven by extratropical wavebreaking onto the Equator, will help to break down the enhanced trade wind regime over the East Pacific, allowing the MJO signal to move past the destructive interference and continue propagating towards the Western Hemisphere. Dynamical models vary on the amplitude of the MJO signal over the subsequent two weeks as it crosses the Western Hemisphere and potentially returns to the Indian Ocean, with most ensemble members gradually weakening the signal. Interestingly, the suppressed phase of the MJO seems insufficient to reverse the low-level westerly wind anomalies across the Indian Ocean. Due to this persistent -IOD structure, enhanced convection is favored to persist across portions of the Indian Ocean basin and Maritime Continent despite any MJO influence. MJO activity teleconnects effectively into the northern hemisphere midlatitude pattern during the boreal winter months, with Pacific events tied to pattern changes favoring a transition towards negatively phased NAO (North Atlantic Oscillation) blocking events and increased troughing over the eastern US. A pattern flip reflecting these signals appears likely to occur in early January. One tropical cyclone developed during the past week, Tropical Storm Pabuk, which formed on 23 December over the South China Sea. Currently downgraded to a tropical depression, Pabuk is forecast to meander close to the southern coast of Vietnam before dissipating under unfavorable atmospheric conditions. During the Week-2 period, despite an unfavorable positioning of the MJO suppressed phase, the low frequency base state may help contribute to tropical cyclone development in a few basins. There is a 40-percent chance of development indicated in the vicinity of the Philippines, either over the northwestern Pacific or the South China Sea. Additionally, there is good model support for a potential tropical cyclone developing over the southern Indian Ocean, though ensemble members are not clustering on a single location. Development is also possible in the vicinity of the Kimberley Coast of Australia, though this region has the lowest confidence. Tropical cyclone development in all of these same regions remains possible during Week-3, with 20-percent chances depicted. As the remnant MJO signal returns to the Indian Ocean, its destructive interference will gradually decrease.

Forecasts for above- and below-average precipitation are based on an anticipated continuation of the -IOD and developing La Niña base state, and an MJO propagation across the Western Hemisphere during Week-2, and possibly the Indian Ocean during Week-3. A skill weighted consensus of dynamical model guidance was also utilized. Above-average temperatures are possible for portions of Brazil and northern Australia during Week-2, with heat persisting across Australia during Week-3. An outbreak of cold air into the central and eastern United States is favored for Week-3. For hazardous weather conditions in your area during the coming two-week period, please refer to your local NWS office, the Medium Range Hazards Forecast produced by the Weather Prediction Center, and the CPC Week-2 Hazards Outlook. Forecasts made over Africa are made in coordination with the International Desk at CPC.